The drive out to the cache is just as interesting as the cache itself. The big brick castle is Winehaven, once the largest winery in the world, later a military fuel depot, currently abandoned. When you reach the cache you will have a great view of the East Brother Light Station. Nice spot for a picnic!
To approach the cache location, take the Western Drive exit from 580. It's the last exit, just before the Richmond Bridge toll plaza. If you're coming from Marin, you have to pass the toll booths, get off the freeway and then back on going west to find the Western exit.
The cache container is smallish -- bring small goodies.