Corinthia is bounded by water on two sides and mountains on the others. The Gulf of Corinth opens to the northwest, its blue surface visible from the coastal highway that runs between Corinth and the seaside town of Xylokastro. To the east, the Saronic Gulf faces Athens, which is close enough that some municipalities on Corinthia's eastern edge are now considered Athenian suburbs. The Isthmus of Corinth — the thin neck of land connecting peninsula to mainland — sits just east of Corinth city, where the canal cuts through at a depth that allows ocean-going vessels to pass.

Inland, the terrain rises quickly. The tallest peak in Corinthia is Mount Kyllini in the west, and the largest natural lake is Stymfalia in the southwest — famous in Greek mythology as the home of the Stymphalian Birds that Heracles was tasked to drive away, and today protected as a nature reserve under the European Natura 2000 program. The contrast between the settled, fertile coastlands and the rugged interior defines daily life across the region.

The geology beneath Corinthia is active. The Corinth Fault and the Poseidon Fault run through the region, part of a broader seismic zone that has shaped the landscape through successive earthquakes over millennia. The low-lying coasts enjoy mild Mediterranean winters and hot summers, but the mountains see genuine cold and occasional snow. The land is not stable — earthquakes have destroyed and rebuilt Corinth more than once across its history.

Fire has also played its part. On July 17, 2007, flames burned through forests around the historic Acrocorinth, the great rock fortress that looms above the ancient city site. The fire was one of many that swept across Greece that summer, but Acrocorinth — visible from the coast, from the highway, from the approaching hills — gave the destruction particular visibility. The castle survived.

Ancient Corinth stood at the center of Mediterranean commerce for centuries. Merchants who wanted to avoid the dangerous passage around the Peloponnese paid to have their goods — and sometimes their ships — hauled overland across the isthmus on a paved trackway called the diolkos. Corinth collected tolls at each end. The city grew wealthy, then powerful, then famous enough to be mentioned by every major ancient historian and to send a delegation to Delphi. Homer praised it. Paul of Tarsus wrote letters to its Christian community that became part of the New Testament.

The modern city of Corinth, rebuilt on the coast after a devastating earthquake in 1858 destroyed the old inland settlement, is considerably more modest. With a population of 30,816 in the 2021 census, it is the regional capital — followed by Loutraki at 12,212, Kiato at 9,907, and Xylokastro at 5,378. The ancient ruins, including the Temple of Apollo and the Acrocorinth fortress, lie a few kilometers from the modern center.

Loutraki has been drawing visitors to its thermal springs since antiquity, and continues to do so. The resort town on the northeastern coast of the Gulf of Corinth is Corinthia's second-largest city and its most conspicuously touristic. But Corinthia's deeper draw is archaeological. The region contains the ruins of Nemea — once one of the four sites of the Panhellenic Games alongside Olympia, Delphi, and Isthmia — along with the sanctuaries of Sicyon, the Heraion of Perachora on the peninsula above the gulf, and Acrocorinth itself.

These sites are spread across varied terrain: Nemea's sanctuary sits in a green valley in the inland hills, Perachora occupies a dramatic promontory above the sea, Sicyon spreads across a plateau above the coastal plain. Each represents a different moment in the long story of Greek civilization finding places to honor its gods and hold its games.

The eastern coastlands of Corinthia grow olives, grapes, tomatoes, and vegetables in cultivated strips between the sea and the rising hills. The region's economy has diversified over the decades — manufacturing and services now matter as much as agriculture — but the land remains productive and the agricultural identity runs deep. Corinthian currants, a small seedless grape variety named for the city, were once among Greece's most valuable exports and gave English the word 'currant.'

The A8 motorway, known as the Olympia Odos, carries heavy traffic between Athens and the Peloponnese across Corinthia's territory. The road first connected the two in the 1960s — the section east of Corinth opened in 1962, the western section in 1969 — and the improvement in transport links drew Corinthia further into Athens's economic orbit. That pull has only grown stronger in the decades since, making Corinthia simultaneously one of the oldest settled landscapes in Greece and one of the newest extensions of the capital's metropolitan reach.