Summer ain’t summer without swimming, and East Bay insiders know that the best place for an afternoon of old-fashioned water play is the Richmond Municipal Natatorium — fondly called The Plunge — an 87-year-old treasure in the Point Richmond historic district. At 160 by 60 feet, the Plunge offers plenty of room to spread out. It boasts an open truss ceiling, like the one at San Francisco’s now-defunct Sutro Baths, and a mural by local artist John Wehrle that depicts a serene blue lagoon under a cloud-studded sky. Devotion to the Plunge runs deep: Even after it was damaged in the 1989 Loma Prieta earthquake, residents continued to use it, despite city warnings, until 2001, when it was finally closed for renovation. Reopened in 2010, the Plunge is now considered one of the greenest public pools in the country, using solar heat to warm its 324,000 gallons of non-chlorinated saline water. And it’s affordable: $5 for adults and $3 for kids. So grab your suit, your goggles, and that flowered pink swim cap Grandma used to wear and head to Richmond for a plunge you won’t forget.