The Donner Pass Summit Tunnels are a series of abandoned railroad tunnels from the original Central Pacific transcontinental railroad, drilled through the granite ridge above Donner Lake in the 1860s. They are now accessible for hiking and exploring — you can walk through the original Summit Tunnel, a dark bore through granite with occasional shafts of light from ventilation openings, and emerge on the other side of the ridge with views in both directions.
The site is reached by a moderate hike from the Pacific Crest Trail trailhead off Donner Pass Road. The tunnels are unrestricted and unlit — bring a headlamp. The old Central Pacific roadbed above the tunnels is also walkable and gives a sense of the engineering achievement required to push a railroad across the Sierra Nevada. The modern I-80 freeway cuts through the same pass below, but the old road is quieter and more historically resonant.