The Kokoda Track is in Papua New Guinea.
What is now known as the Kokoda Track was a collection of trails and trading routes used by villagers to cross the Owen Stanley Range and travel from the south to north coast of Papua New Guinea for hundreds of years, and in the 19th century by Europeans keen to reach the goldfields on the northern half of the island.
Even today, there is not a single route from what is now known as Owen's Corner in the south to the Kokoda Valley in the north, but alternative tracks that go through different valleys and different villages for about 96 kilometres. The most commonly used series of tracks follow about two thirds of the original track fought over.
The track became famous during the Second World War when troops of the 39th Australian Infantry Battalion and Japanese Imperial Forces fought a long and arduous battle along its route to prevent the Japanese forces from reaching Port Moresby in the south, and thus a potential starting point for an invasion of mainland Australia.
Since then, and particularly in the past two decades, walking the Kokoda Track has become a rite of passage for Australians of all ages, on a par with visiting Gallipoli on Anzac Day. It has become one of the most popular activities in Papua New Guinea, attracting over 4,000 walkers a year, most intensively over Anzac Day in late April when the track is at its busiest, and then over the dry season from May to October.
Certainly it is difficult for Australians and Japanese to not shed a few tears when they reach the war memorial site at Isurava.
The Kokoda Track is a tough but doable hike in subtropical rainforest. A sufficient level of fitness and suitable equipment are critical for a safe and enjoyable experience.
Before walking the Kokoda it is important to carefully assess how fit you are. There are incidents of people dying of heart attacks from over-exertion, which has led to many operators requiring a medical evaluation before walking the track. There are several speeds at which one can walk the Kokoda, taking from a leisurely twelve days to a gruesome 16 hours, 34 minutes and 5 seconds, the world record held by local porter Brendan Buka. Basically the most important thing is that you have fun doing it. Going too fast isn't fun, but taking it too slow can be boring also if you have to wait for the others all the time.
For seasoned hikers the Kokoda Track is very doable, but if you’re not used to walking ~15km a day over uneven terrain then this is going to be a challenge... Groups typically spend ~60 hours in total walking up and down steep, often muddy hillsides, with flat sections a rarity.
In terms of equipment a good pair of hiking boots are critical, and bring enough socks for a fresh pair each day. There are plenty of streams to wash clothes in but especially in the lower parts of the track the humidity makes it difficult to dry things. Inspect your feet every day and apply blister packs at the first sign, to prevent more serious issues developing. The other critical piece of equipment is a pair (much better than one) hiking poles, as the track is often rooty and muddy. You'll spend most of the time looking at your feet to ensure that you don't trip over, and poles help hugely with balance and control.
Other must bring items are anti-malarial drugs as there are mosquitoes around, though the numbers vary significantly by season, warm layers for the higher parts of the track where you camp at ~1,900m, water purification tablets to treat the stream water, a travel towel / sport chamois to dry after camp showers / streams, swimming costume for washing in streams, an inflatable mattress, a head lamp, ear plugs, hiking sandals for river crossings, sun protection (lotion, hat), insect repellent, toilet paper as there is none along the track (though every campsite / village has at least one long-drop), hydralytes to rehydrate after sweating from the exertion and humidity, a light sleeping bag though a sleeping bag liner is fine for the lower parts of the track, spare set of dry clothes for the campsites, and dry bags to keep your things dry if it rains.
Useful items to consider taking include a solar charger as there is no electricity along the track, an inflatable travel pillow, a Z seat for comfort, and an old toothbrush to clean your boots after the walk if you're returning to Australia or New Zealand, given the strict border controls.
If time or stamina is a problem you can join the Kokoda Track in the middle. Airlines PNG  flies to Efogi, Kagi and Manari and from Port Moresby, as well as to Kokoda. The southern starting point can be reached by road from Port Moresby. Kokoda can also be reached by road from Popondetta, which receives regular flights by Air Niugini .
The vast majority of people walk the track as part of a guided group. There are over 80 operators, almost entirely Australian owned, who run tours ranging from six to twelve days long. The largest / best known operators include Adventure Kokoda, Escape Trekking, Kokoda Spirit, and No Roads Expeditions. There are a handful PNG owned operators including South Sea Horizons (used by Intrepid Travel), KoTreks, and Buna Treks and Tours, who ensure that all money involved stays in PNG. Expect to pay between AU$3,000 and AU$5,000 for an all inclusive trip (excluding flights). It pays to understand the size of the groups, as they can range from 3 to 20 people, making a large difference in the time taken to walk each day, and access to facilities at campsites.
The track can be walked independently but is not recommended from a safety perspective, both in terms of the terrain, and walking without a guide in the bush in PNG can be risky (see stay safe below).
Almost all itineraries include going through Imita Ridge, Ofi Creek, Nauro, Menari, and Templeton's Crossing. Different companies have different guiding styles and areas of focus. Many employ ex-military tour leaders / historians to provide a detailed understanding of the 1942 Kokoda campaign, while others focus more on the local communities.
There are many campsites along the track, which are very similar in set up though the quality does vary. They have two huts for the crew, to cook and sleep in, one hut for the group to use, a grassy area for tents, usually a shower or at least a swimming hole, and one or two long drop toilets with standard green seats.
There is very little wildlife along the trail, expect to hear some birds but sightings are rare. As the only way to cross the Owen Stanley Range is by foot or plane expect to hear a few flights passing overhead. There is some litter along the track, but it is nowhere near as bad as many countries, and reflects the difficulty of disposing of rubbish in a remote area with limited community services. There are a few clinics and primary schools in the large villages, often funded by the Kokoda Initiative, a partnership between the Australia and Papua New Guinea governments.
There are four official museums along the track, at Efogi, Kokoda, Isurava Memorial, and Alola. They’re not guaranteed to be open though, depends if the person with the keys is around. Off the main track there are a few spots where locals have found ammunition from 1942 and stacked it in neat piles. To visit usually costs 10 Kina, if there is someone there to take the money.
The track can be walked in either direction, but the most popular is from Kokoda to Owen's Corner as it is regarded as slightly easier (though day two has a huge hill to climb up to Alola), and ends with a visit to the Bomana War Cemetery on the way from Owen's Corner back to Port Moresby. Walking from Owen's Corner to Kokoda is quieter, and finishes with the scenic flight from Kokoda back to Port Moresby, following the path of the track below, putting the walk into perspective.
By far the most popular time of the year to walk the Kokoda Track is over ANZAC Day, a public holiday in Australia and New Zealand held on the 25 April. This is toward the end of the wet season with 2-3 wet days a week to be expected. The actual Kokoda battle was fought between July and November 1942, during the dry season when rain is much rarer. It can rain anytime of the year though, particularly in the higher parts of the track.
There have been a number of deaths on the Kokoda Track in recent years. In 2009 a small plane flying a group crashed killing 13 people, and during the same year four walkers died on the track from medical issues. In 2016 a British man and an American woman walking the track without a guide were attacked near Templeton's Crossing II campsite. To put these incidents in context thousands of people walk the track every year, and there have been no issues with guided groups. The biggest risks are injury from slipping or tripping on the track, health challenges from not being fit enough, and acclimatising to the tropical heat and humidity.
Kokoda Track trips start and finish from Port Moresby, which is worth a day or two to explore. On the way to / from Owen's Corner all trips stop at the moving Bomana War Cemetery, home to the graves of those who died on the track during WW2.