Corinth

Ancient Corinth has its own ties to Greek mythology. When Jason returns with the Golden Fleece, he docks his ship, the Argo, in Corinth and gives thanks to Poseidon, patron god of the city. Poor Sisyphus, King of Corinth, offends the gods, and each day Sisyphus is doomed to push up a huge bolder up the hill, only to have it roll back down. Bellerophon captures the winged horse Pegasus drinking from a fountain in Corinth. After a visit to Corinth today, kids can imagine where the myths spring forth.

Acrocorinth - Acrocorinth is just a great and glorious castle, high on a hilltop above ancient Corinth. According to legend, it's here that Pegasus came to drink from the spring. The site has been a fortress since the 6th century B.C., but what you'll see are the well-preserved medieval fortifications, built by the Franks, Turks, Byzantines, and Venetians. Acrocorinth is big, 2 kilometers of walls, 575 meters high, and there's lots to explore.
The castle is protected by a dried up moat (there's a bridge over it), then three sets of gates and watchtowers - as gatekeeper for the Peleponnese, this castle needed protection. Each gate was built at different times, and the innermost gate has the oldest foundations.
Once inside, you can ramble freely. Go out on the ramparts, to look out over the fields below and the Gulf of Corinth in the distance (and imagine you are king of the castle). Climb up to the small Venetian chapel, you can peer inside to see hanging lamps and silver icons.
The flat grassy area with an olive tree is the site of large Byzantine cistern - there are three gratings where you can look down and see water below (not a lot, but it's there). You can climb up the little stone tower, shaped like a minaret - the steps are small and the ceiling is low, and it's completely open at the top (no railing), but it's fun to poke your head out. The olive tree is a perfect place for a picnic (when we were there, a bunch of young people were picnicking and tossing around a soccer ball on the grass).
Older kids will want to keep climbing up the hill to the square-shaped Frankish keep, perched on the promontory. (Past the keep, the trail is narrow and rocky, and there are large openings in the rock walls). Panoramic views of the surrounding countryside and a feeling that you're "king of the mountain."
Ancient Corinth - If you can't get enough of old ruins, or want to see the remains a Roman city, visit the archeological site of ancient Corinth. Corinth was a bustling Greek city for centuries, strategically placed at the isthmus between the Peleponnese and mainland Greece, and in the and in the Roman era, Corinth replaced Athens as the capital.
The highlights of the ruins is the Temple of Apollo, a pretty well preserved temple from the 5th century BC. Don't miss the Fountain of Peirene - it was once a large public fountain (fed with natural springs) at the entrance to the Agora/Forum, and steps leading down to an ancient sacred spring, where pilgrims would consult Apollo.
Outside the ruins, across the street from the Temple of Apollo, is a small playground with swings and play structure.
Corinth Canal - The Peleponnese is divided from mainland Greece by a narrow isthmus, and this bitty piece of land was a big inconvenience for boats going between the Gulf of Corinth and the Saronic Gulf. In the 6th century, Periander tried digging a canal, but found it bit much, and finally in 1893, a "ditch" was dug to allow boats to pass between the two gulfs. Stop at the bridge over the canal to look down into the steep-sided cut through the earth - you can see the geologic layers perfectly.
Or better yet, take a Corinth Canal cruise. Pick up the boat at Isthmia, Wed. - Sat. 10:00am and 5:00pm, and Sun. 5:00pm.