When you say "ground rule," people visualize a one-hopper over the fence. Two bases. But that's not really a "ground rule" because it's a standard rule that applies in every professional ballpark in the land. That's why Jon Miller (correctly) calls that sort of hit an "automatic double" rather than a "ground-rule double."
Real ground rules are a lot more fun, specific to particular ballparks, and here are four of my favorites: