On a rainy Tuesday night in late May, 400 people thought a run through the woods sounded like a good idea. Then they hit the first unjumpable mud puddle and realized this was, in fact, the best idea they'd had in a while. Tiptoeing around the edge was abandoned and the brave puddle pioneer got a cheer and a decorative mud tattoo from shoes to shorts.

Ten kilometers later, the Endless Summer Trail Run Series was fully baptized and the after-party rolling, the music drowned out by hundreds of race stories being recounted at the same time. Remember at the bottom of that big hill … This guy slipped and we all just jumped over him … I was like, what the heck, I'm just blasting through … Oh, there was a clock? … Are you doing the next one?

Endless Summer, now in its third year, consists of five trail runs throughout the summer at four different Twin Cities area parks. Distances range from 5 kilometers to 7 miles. All take place on weeknights.

"This was so much fun; I loved it," said a drenched and beam­ing Kevin Noth, 43, of Bloomington. "It brought me back to high school cross-country. To me, this is summer running. There's so much more to it than a road race — the camaraderie, the pizza, the beauty of the trails. It's just so different."

The modest $25 entry fee for each race includes swag (in this case, a glass), pizza, beer and soda, which, when combined with the post-run glow, form an unbeatable atmosphere that regularly draws the race limit of 400 flushed and chatty off-roaders. The series is well-publicized, the courses accurately measured and marked, and the chip-timed races are staffed with a phalanx of volunteers, so there's actually quite a bit of infrastructure behind this seemingly casual happy hour.

The right combination

John Storkamp, who organizes the series, admits the line between being low-key and obscure is thin, but he seems to have landed on the right recipe; Endless Summer has garnered national attention as the best organized, best attended weekday trail run series in the country.

Storkamp knows all about the transcendence of running through the woods. An accomplished ultradistance trail runner and head honcho of Rocksteady Running Endurance Events, he was approached by Twin Cities Running Company specialty store in 2012 to see if he had interest in reviving a summer race series it co-sponsored with Life Time Fitness. Life Time had established the weeknight trail format, but found that the necessarily small (by road running standards) event didn't align with its business model.

"Over my 20 years of racing, I'd see people run a race, hop in their car and leave," said Storkamp. "We saw a unique opportunity to build community with this series. I mean, the food and drinks afterward are almost as large a focus as the race itself. Most people spend longer hanging out after the race than running it."

Friends Becky Ruud, Kaitlin Lee and Lori Gartner were among the crowd enjoying the post-run socializing. Fit enough to keep up a steady stream of conversation and still run at a good clip, they'd done road races but not the trail equivalent.

"This was cheap, fun, low-key … it was great," Lee said. "Plus, since it's midweek, our husbands can watch the kids. We'll definitely do some more of them."

Endless Summer's midweek timing was mentioned as a stroke of genius by organizers and runners alike. For Storkamp, holding the races then means he doesn't have to compete with the 15 to 20 other races in the area that happen on summer weekends.

First-timer Noth liked that he didn't have to give up a precious Saturday to run a race.

The trail venue is another big part of the appeal. The first woman to finish this race, Margaret Ludick, 30, from Birchwood, Minn., described herself as more of a road runner but loved the opportunity to discover new off-road places to run. "Some of these parks I've never heard of before, but you just show up and it's a blast!"

Storkamp traced the increased popularity of trail running to young people entering the sport. "When I lined up for a trail race in the early 2000s, at 22 I was the youngest by at least 20 years. Now, the number of 20- to 30-year-olds is staggering."

Easy introduction

One stumbling block for trail virgins, though, is distance. A lot of trail races are ultras, longer than a 26.2-mile marathon. Endless Summer's shorter distances are an easy introduction to the sport.

"We've got elite runners using this as a midweek workout, people who've never run on trails and people who walk, which is completely acceptable," Storkamp said.

This race's winner, Jeff MacLellan, 31, of St. Paul is one of those top-level trail runners who uses the series as a workout, when he isn't on call. He's a surgery resident.

The series started in 2012 with three races, went to four in 2013 and 2014, and added a fifth this year.

"I just want to be a good steward of the event and promote the idea of community," Storkamp said. "The trick is to keep veterans involved and, at the same time, to initiate new runners to the idea of racing and volunteering, as a member of the community."

By allowing runners to see the same people, make friends and even stoke rivalries, race series are more effective at nurturing that sense of community than a single event.

"Oh, yeah, we're going to do the others," said a racer in post-race recovery mode, beer in one hand, pizza in the other. "I like hanging out with this crew."

Sarah Barker, a freelance writer, runs from her home base in St. Paul.