TCS New York City Marathon

Run through all five boroughs while total strangers scream your first name off your race bib, four million spectators deep by the time you hit First Avenue — the world's largest marathon isn't subtle about turning 26.2 miles into a citywide party with you, personally, as the guest of honor. It starts on Staten Island, crosses the Verrazzano-Narrows Bridge into a wall of noise, and doesn't really let up until Central Park.

With runners from 130 countries and one of the biggest charity-runner cultures in the sport, solo entry here is barely worth remarking on — everyone around you at the expo, the start corrals, and the finish festival is navigating the same thing alone or with people who aren't running. The city itself does the rest: pre-race pasta dinners, post-race recovery walks through whichever neighborhood you're staying in, and a finish-line high that's genuinely easier to enjoy solo, on your own schedule, than shepherding a cheering squad through subway logistics.

It's expensive by the time flights and marathon-weekend hotel rates land, but as a single bucket-list solo trip, few races anywhere match the scale of the reception you get for finishing.