Mike G
Google
Approaching this from the beach side only to be greeted by a fence and then followed by the realization that you have to walk up to the museum and pay 7€ to get in, I am not going to lie, at first, I was a bit hesitant about spending that money.
But it is totally worth it! The museum is actually really interesting and inviting, they have some really cool stuff on display - and once you are done, you get to go outside and see the landmarks and the cave, get to walk around and on a good day get a great photo opp from inside the cave, with the water reflecting the city on the hill in the background.
My recommendation, however, is to go when it is not as busy - we went on a fairly overcast day off season, but I'm pretty sure that on a nice sunny day, when Sperlonga is filled with tourists, that this place can be quite crowded. In case you do forget to bring refreshments, there is a small vending machine near the entrance that sells water for 0.60€ a bottle, but good luck getting your change - just bring your own supplies and you will be golden.