The Slime Run, Portland

The gritty, dirty fun of mud runs has become popular among runners, but the creators of The Slime Run thought they could improve on the formula. So in their races, they replace that mix of water and wet earth with their own custom formula: a green, slick slime that inevitably covers runners as they navigate a 5K course. After conquering each of four slime zones, they're presented with a relatively simple obstacle, but one whose objective is more difficult when you're coated in slime.

Of course, there's more fun to be had than just getting messy. At the finish line, a runner's party with food vendors, a beer garden, and live music awaits race finishers, as do perks: race medals, mugs, and headbands. At the end of the day, the emphasis is as much on safety as it is on fun, which is why each batch of slime is mixed from hypoallergenic, edible materials and not material left over from the set of Ghostbusters II.