The place
Mount Kilimanjaro, in short.
Kilimanjaro is a free-standing volcano rising straight off the plain, which is why it looks the way it does from a hundred kilometres away. It has three cones. Kibo carries the summit and the remaining ice; Mawenzi is the jagged one you walk past; Shira collapsed long ago and is now the plateau you cross on the western routes.
You walk through five climate zones in about five days — farmland, rainforest, heath and moorland, alpine desert, and finally the arctic zone at the top. Very few places on earth compress that much into that little distance.
It requires no technical skill. There is no rope, no ice axe and no climbing on any normal route. What it requires is time, because the only thing that reliably gets people to the summit is spending enough days going up slowly.
That is the single most important thing on this page. Success on Kilimanjaro tracks the length of the route almost exactly. The five-day Marangu climb is the cheapest and the one that fails most often. If you are going to spend this much money and this much annual leave, buy the extra days.