What kind of person can run in a tiny, maddening circle for 24 hours straight? I visited the legendary D3 marathon to find out.

July 1, 2023

D3 is a very particular kind of ultramarathon, a broad category of races that includes anything longer than 26.2 miles. The most common versions are based on distance, and are run on trails or roads. But there are also time-based races, ranging mostly from six hours to six days. You run as far as you can in the allotted time, and as races stretch on, you must eat, change clothes, rest, sleep, and do everything else you need to do to keep running. Because measuring every runner’s distance is essential, these races tend to take place on short loops which runners run over and over. Slate