Poseidon hotel is located next to the harbor and prides itself as the gem of Spetses. Built in 1914 by the national benefactor Sotirios Anargyros, it was a key pillar in the island's development plans, along with Anargyrios and Korgilanios School. Its creation was based on designs by the architect Panagiotis Zizilas, which were inspired by respective hotels cosmopolitan Côte d'Azur.

Posidonio in its heyday was the largest and most impressive hotel in the province and hosted many foreign distinguished guests as well as leading figures of Greece, like Eleftherios Venizelos.
Today Poseidonio is fully renovated, inviting the visitor to admire its exterior and, if he can afford to, enjoy its hospitality.