Epidavros is worth seeing but is a tricky place to get to. Most visitors go by coach from elsewhere on the Peloponnese. Maybe from Methana, which is almost an island. We sailed from Aigina to Epidavros port (and were given 24 hours to leave by the Port Police) but there's no ferry AFAICS and the port is not worth staying in (but perhaps I'm biased.) There may be some ferries during the Epidavros Festival.

I suggest staying in Navplion, which is an pleasant and interesting town. We first went when the coach from Kalamata to Poros broke down and we spent several hours there. There's a bus from Athens too.

Trizonia in the Gulf of Corinth was a nice little island...