CC BY-SA 4.0, Eleni Kalogeropoulou, via Wikimedia CommonsLandmark· Paralio Astros· Greece — Ionian, Saronic & Argolic
Astros Frankish Castle
37° 25.1′ N · 22° 46.0′ E
The ruined castle on the hill above the harbour, fortified in the Ottoman era and rebuilt in 1821–1825 by the Zafeiropoulos merchant brothers, whose garrison of about 1,200 held off Ibrahim Pasha's army in 1826. Walls up to 6 m high, cisterns and the brothers' ruined houses remain.
Practical
Coordinate from OSM ('Κάστρο Παράλιου Άστρους'); Greek Wikipedia gives 37.418392, 22.767044. Open site, free, accessible year-round; reach the east gate from the upper village — a 10-minute climb from the quay. Views over the gulf to Nafplio and the Astros plain. Despite the common 'Frankish' label, Greek Wikipedia dates the visible works to the 17th–19th centuries.
Best for
Short sunset climb from the quay