According to John Muir, the Hetch Hetchy Valley was once every bit as beautiful as neighboring Yosemite Valley to the southeast. However, the renowned conservationist ultimately lost his struggle to save the slightly smaller Hetch Hetchy Valley from development and, in 1923, the O’Shaughnessy Dam began diverting water to a thirsty San Francisco, nearly 170 miles away. The controversy continues to this day, with environmentalists calling for demolition of the aging concrete structure every few years—to no avail. Still, if you’re craving some solitude, Hetch Hetchy is a worthwhile detour while inside the park. Just below the dam, you can take a short but steep hike down to the Tuolumne River, which runs through the lovely Poopenaut Valley. If time and budget allow, treat yourself to a night at the nearby Evergreen Lodge.