A 55-year-old woman making her way through the crowd is topless, with her generous proportions painted white, the words “Ghost of Weird Austin” written across her torso. While some people stop her to chat or take photos, others barely seem to notice her. After all, there are plenty of other attendees in various states of creative dress — and undress — enjoying a day at the park in their own ways.

This scene is hardly unusual at Eeyore’s Birthday Party, which has been held each spring since 1964, making it arguably the longest-running celebration in festival-heavy Austin, Texas (it is rivaled in age only by the Zilker Kite Festival). But unlike the city’s more well-known events — including South by Southwest and Austin City Limits — the one-day Eeyore’s Birthday celebration is volunteer-run, charges no admission fees, and benefits local non-profit groups through the sale of food, drinks and merchandise, which can be purchased at affordable prices. That openness and accessibility draws the free spirits that help make the festival a symbol of the city’s well-worn slogan: “Keep Austin Weird.”

Named for the Winnie-the-Pooh story where the sad donkey’s birthday has been forgotten, Eeyore’s Birthday was started by two University of Texas students, Lloyd Birdwell and Jean Craver, both now deceased. It was initially celebrated in Austin’s Eastwoods Park with a maypole, guitar playing, costumes — and a live donkey. Although it began as a way for University of Texas students to celebrate spring before the onset of final exams, Eeyore’s Birthday soon attracted a broad swath of Austin residents. “Originally it was a sorority and fraternity thing, and then it opened up to everybody at UT and then to the community of Austin,” says Jim Ayres, a retired University of Texas professor who was involved with hosting the celebration from 1965 through the late 1970s.

“We had parents bringing very young children. At the other end, we had some very old people in their 70s and 80s dressed up in costumes and having a great time, too. So it wasn’t all students,” Ayres says.

By the festival’s 10th anniversary, “Lady Bird” Johnson and Lynda Bird Johnson, wife and daughter of President Lyndon Baines Johnson, were among those in the huge crowds. That also meant Secret Service members and a heavy police presence around the festival’s periphery. “We invited famous people all the time, but we didn’t expect them to show up,” Ayres says.

With crowds came some changes. After the parks department became unhappy with the number of cars around Eastwoods Park, in 1974 the festival relocated to 42-acre Pease Park, also within walking distance to campus. “That’s where the numbers really increased because it was more visible, more open,” Ayres says.

Thousands of people attend the celebration every year. Today, the festival features live music, drum circles, acroyoga, as well as an egg toss and other family-friendly games. There are costume contests for both kids and adults, which last year included a woman wearing a hoop skirt covered in pots and pans and a man carrying a large “Pot Notch Hempcoal Hashburgers” sign — a play on the logo for a local hamburger joint — topped with a green marijuana leaf. Despite the city’s influx of new residents, funky Austin is alive and well.

Several years ago, before he passed away in 2014, the current organizers contacted festival founder Birdwell, who was living in Dallas, and invited him to attend. “He had a great time,” says Scott Sexton, 51, current president of the Friends of the Forest Foundation, the non-profit that runs Eeyore’s Birthday. “Two weeks later, he came back for the picnic, where we provide free food and beverages for the volunteers. He cornered me and said, ‘How do you do it, Scott? It’s nearly 50 years later and this still feels like the event I went to in the 60s.’ I was amazed he thought that. But I realized it’s because we don’t have fences, we don’t have rules everywhere and we don’t have vendors trying to make as much money as they can off people.”

The costumes have also remained a constant, although some decades have seen more elaborate outfits that others. “In the 80s, one of my favorite attendees dressed as Cleopatra and he was hauled in on a palanquin by four very light dressed males. It was just gorgeous,” says Lori Moore, who has been secretary for Friends of the Forest’s board for about two decades. “Another time, he was Marie Antoinette with speakers in her skit playing ‘La Marseillaise.’ That was during the AIDS epidemic, and I’m afraid that person may have died. But sometimes you can still see that over-the-top thing. I enjoy that a lot.”

“It’s the best people watching, ever. To this day, I will sit down for 30 minutes and just watch people go by,” Moore says.

The festival has taken on a life of its own, according to the current organizers. “We don’t advertise, but the last Saturday in April, you’re going to have people in Pease Park,” says Sexton. “The question is: Do you want to have it organized by Friends of the Forest Foundation or another group or do you just want people to show up? The event will to continue to happen, whether we’re involved or not.”

New generations of Austin residents enjoy the festival each year. A pair of mothers who were first-time visitors brought their young children after hearing recommendations through a local network of mothers on Facebook. “We weren’t surprised by anything at the festival — this is Austin,” says Jessica Roy, 27. “Everyone knows to keep Austin weird. If they don’t like it they can go to Dallas.” Her sister-in-law agrees. “The kids are going to be raised in Austin, so they should be exposed to everything the city offers,” says Elizabeth Tsui, 33.

While the city continues to grow, Eeyore’s Birthday offers a way to keep the spirit of unusual Austin alive. “We’ve got to keep it weird and keep it happening,” says the woman in white body paint, Lola Estes, who hasn’t missed a celebration since 1978. She’s doing her part. “Every year, I make 60 brownies to give to every topless woman I see.”

Eeyore’s Birthday will be celebrated this year on April 30, 2016.