Palaiokastro of Leros, also known as the Castle of Lepida, is the oldest fortification monument on the island. It is situated on the southwestern side of Leros, near the coastal settlement of Xirokampos, built on the summit of a steep hill at an altitude of about 70 meters. Its strategic position offered full visibility over the maritime passage between Leros and Kalymnos, serving as a crucial lookout for early detection of hostile raids.

The oldest sections of its walls date back to the Classical and Hellenistic periods (4th century BC) and are constructed using the famous isodomic masonry technique, featuring massive, finely carved Cyclopean stone blocks. During the Byzantine era, the fortifications were reinforced, and the castle was utilized as a secure refuge for the local population. Within the archaeological site, ruins of ancient structures, subterranean water cisterns, and the picturesque, later-built Church of Panagia (Our Lady) of the Castle-also known as Panagia Palaiokastrini-can be seen, which stands directly upon the foundations of an ancient pagan temple.

The ascent to Palaiokastro is made via a well-defined stepped path starting from the area of Xirokampos. The hike rewards visitors generously, as the summit offers an outstanding panoramic view of the endless blue Aegean Sea, the coastlines of neighboring Kalymnos, and the surrounding island landscape, beautifully merging rich history with natural elements.