Bad Archaeology has a nice picture of the newly rediscovered Lupercal, the cave where Romulus and Remus were supposedly born. The cave is actually a domed and frescoed chamber under the Palatine — and what frescos!
The post also claims that the Lupercalia was abolished by Pope Gelasius. Looking around the web, this seems to be based on a letter by that Pope to the senator Andromachus (perhaps ep. 100). Is this online anywhere, I wonder?