Piraeus is a port city and the best reason to eat here is the seafood — fish landed daily, served at restaurants that line the Mikrolimano harbour and the main waterfront. Greeks eat late; restaurants fill up from around 8pm.
Jimmy and the Fish is a well-regarded seafood spot right on the dock at Mikrolimano, with seating overlooking the water. Prices are on the higher end. Margaro is known for its shrimp and koutsomoura (red mullet); the menu changes with the catch. Ammos and Dourambeis are reliable alternatives along the same stretch.
For something cheaper, the souvlatzidika around the city do good grilled meat. Vosporos overlooks a small bay and handles both grilled food and souvlaki at moderate prices. Hilies Kai Mia Geuseis is a simple takeaway-style place with tables, good food, and low prices. Iasonas 42 is a family tavern popular with locals for its straightforward regional cooking.