In geography, enclaves and exclaves are territory which (respectively) is surrounded by land which belongs to some other nation or is separated from its own parent country by foreign territory.
Conversely, Hyder, Alaska (or even the entire state of Alaska) may qualify as an exclave, as the only overland access from the Lower 48 runs through British Columbia or other Canadian territory. There are also semi-exclaves (where the territory is only reachable by foreign land or international waters) and pene-exclaves (which are only reachable over foreign land or by crossing domestic waters).
An enclave differs from a country which is merely landlocked. Landlocked Switzerland has no direct access to the sea, but has multiple neighbours which each have viable seaports – so no one nation can cut off all access to Swiss territory from abroad.
Wikipedia has an extensive list of these, but no list is comprehensive.
While there are political implications (for example, Lesotho was not free to embargo South Africa during the darkest days of the apartheid era, since it's entirely surrounded by that country), the primary impact on travel is to require border crossing (and all of the strange customs which go with it) for what otherwise should have been either a domestic trip or a trip which could have averted transit through a third country. That can cause problems during events such as the COVID-19 pandemic of 2020-21, when many borders are restricted or closed.
There's also the risk that a war could create enclaves where none formerly existed, as a populated place is entirely surrounded by an adversary. Some of these are also the result of errors when originally drawing national boundaries, or are created (or eliminated) as boundaries change over the years.
The same terminology has also been used for sub-national or even municipal entities (Piedmont is an enclave of Oakland, California, etc.). The term enclave has also been used figuratively along cultural, economic or identity lines, such as to identify "Chinatown" as an Asian cultural enclave within a city on some other continent, to identify a "gay ghetto" as an "LGBT enclave", or to identify a neighbourhood of multi-millionaires as an "enclave of the rich" within a larger city where others are not as wealthy.
Ada KalehDanube, at a point where the river formed the border between Romania and Serbia. Its inhabitants made a living by agriculture, fishing, and smuggling.
Since the area was overlooked at the 1878 Congress of Berlin, at the conclusion of which Romania gained its independence from the Ottoman Empire, the island unintentionally remained as an Ottoman Turkish exclave, with the nearest location in the Turkish "mainland" (after 1913, when the current borders in the Balkans were more or less set) being Edirne, about 480 km / 300 mi to the southeast as the crow flies, and two countries apart. Being full citizens, the islanders could vote in the Ottoman general elections of 1908, and the Ottoman government kept asserting its sovereignty by regularly assigning a mayor and a judge.
Turkey forwent all of its claims to the island in favour of Romania, thus ending its exclave status, in the 1923 Treaty of Lausanne, under the terms of which the western powers agreed to recognize the newly-founded Turkish Republic. However, the inhabitants, comprised completely of ethnic Turks, were allowed to stay, and were to become Romanian citizens from that point on.
The island ceased to exist as it was submerged by the Iron Gate Dam lake, completed in 1970 — in collective memory, the loss of Ada Kaleh is one of the most evocative instances regarding the dam's construction. The Romanian government's attempt to build a 'new Ada Kaleh' by moving some of the structures to a nearby island not effected by the dam lake proved futile, and while some of the locals, along with the carpet gifted by Ottoman sultan Abdülhamit II (r. 1876–1909) to the sole mosque of the island, relocated to Constanta, a Romanian city with a relatively large Turkish community, most opted for resettling in Turkey.
- Baarle is a Gordian knot of enclaves nested and entangled inside of other enclaves, so that a fragment of the Netherlands might be within a piece of Belgium which is in turn surrounded by the Netherlands. There's a complex set of legal agreements which go back centuries; the nationality of any individual house or building is typically determined by the location of its front door relative to the multiple, confusing boundaries.
- Gibraltar is an exclave of the United Kingdom, separated from the motherland by Spain and water.
- Kaliningrad is an exclaved Russian seaport which is not accessible overland without crossing European Union territory.
- Nakhchivan is an exclave of Azerbaijan which borders Turkey to the northwest, Armenia to the north and east and Iran to the south.
- Campione d'Italia is an exclave of Italy surrounded entirely by the Swiss canton of Ticino. As both Italy and Switzerland are part of the Schengen Area, and Ticino is an Italian-speaking region, you may not even notice that you have entered another country.
- The Vatican City and San Marino are enclaves surrounded by Italy.
- Monaco is an enclave with a Mediterranean coastline and otherwise surrounded by France.
- Brunei consists of two enclaves, connected by a bridge that traverses some Malaysian waters. Except for their coastline on the South China Sea, they are surrounded by the Malaysian state of Sarawak.
- The Musandam Peninsula is an exclave of Oman that borders on the emirates of Ra's al Khaymah and Fujairah, which are members of the United Arab Emirates, and the Straits of Hormuz.
- Oecussi is an exclave of East Timor that borders only on West Timor, Indonesia and the Savu Sea.
- Singapore has an exclave, the island of Pedra Branca, that is completely surrounded by Malaysian waters belonging to the state of Johor, on the western edge of the South China Sea. It was the subject of a territorial dispute between Singapore and Malaysia, and was awarded to Singapore by the International Court of Justice in 1998. It is a restricted area, and special permission is needed to access the island. In addition, there is also the island of Pulau Pisang off the west coast of Johor, which while undisputed Malaysian sovereign territory is home to a lighthouse and an access road leading to it that are administered by Singapore.
- Cabinda is an exclave of Angola that is separated from the rest of the north of the country by part of the Democratic Republic of the Congo.
- Ceuta and Melilla are two Spanish exclaves that border only on Morocco and the Mediterranean.
- Lesotho is an enclave surrounded by South Africa.
- Much of the Alaska Panhandle is only accessible overland through British Columbia, even for voyagers arriving from elsewhere in Alaska. The Alaska Marine Highway System is a viable alternate to reach most exclave points, except for Hyder (which has only the road to Stewart BC or the float plane which brings the mail from Ketchikan).
- Campobello Island is accessible overland by a bridge from Lubec, Maine. This gives it exclave-like characteristics as the only access from within New Brunswick is a pair of seasonal ferries through Deer Island to the Canadian mainland.
- The Northwest Angle is a tiny recreational fishing outpost in northern Minnesota, but the only access to this exclave (short of taking a boat or floatplane across Lake of the Woods) is the lone, lonely Winter Road to Manitoba. As the Angle is a dead end, the customs house is an unattended booth with a webcam.
- St. Regis (near Cornwall-Massena) is a Quebec peninsula severed from New York State's mainland by the 45th parallel. (Effectively, this tiny exclave is Point Roberts, Washington or uninhabited Elm Point, Minnesota in reverse – but with everything further complicated by its location in Akwesasane, part of the Mohawk native first nation, which spans part of Ontario, Quebec and New York State. Add the St. Lawrence River, Ontario's international boundary, to make the confusion complete.)
- The village of Atlin, British Columbia, is only accessible by road through the Yukon Territory.
- The village of Tungsten, Northwest Territories is only accessible by road through the Yukon.
- Copacabana is an exclave of Bolivia, close to the capital La Paz but reachable from Bolivia only by ferry across the Tiquina Strait. A peninsula in Lake Titicaca, it's actually joined to Peru's mainland.
- The sparsely-inhabited Jervis Bay Territory occupies a coastal peninsula. It is not part of the Australian Capital Territory, but the laws of the ACT do apply to it. Jervis Bay Territory is administered by the government of the ACT and thus it is a pene-exclave, accessible only by travel through New South Wales. All of it is now a national park, and NSW Parks passes aren't valid here
- A section of North Tweed is only accessible through a road which cuts through two states, with one side in the state of Queensland with the other being in the state of New South Wales. However, the side of the road that goes to North Tweed is on the Queensland side, and the road that comes out of North Tweed is in New South Wales meaning if you're going to North Tweed by car, you have no choice but to go through the Queensland section. However, if you walk, it is possible to avoid the Queensland section entirely.
- Another one in Tweed Heads, there are also two residential streets (Kirra Gr and Coolangatta Rd) with no access through their home state New South Wales, and the only way to access them is via Queensland. You could go through the NSW side if you climb the backyards of the locals, but... that's not practical
- The Torres Strait Islands are Australian islands but completely surrounded by Papua New Guinea's territorial waters. This was the result of an agreement which was made just after Papua New Guinea's independence from Australia in the 70s. The islands include Anchor Cay, Aubusi Island, Black Rocks, Boigu Island, Bramble Cay, Dauan Island, Deliverance Island, East Cay, Kaumag Island, Kerr Islet, Moimi Island, Saibai Island, Turnagain Island, and Turu Cay,