Ayia Marina, a small coastal settlement and one of the two harbors in the island, has expanded with time and joined up with Platanos, the oldest settlement and the capitol of the island. It is the administrative and commercial center and has the most tourist activity. From afar it looks like a small city spread out in an amphithetrical shape between two mountain slopes with white houses which stretch from the waterfront all the way to the foot of Kastro. But the nearer the visitor gets the more the "city" reveals its charms one by one.

Many traditional two-storey houses have been preserved in Platanos and among them are numerous mansions so densely built that they create narrow, picturesque lanes which lure the visitor down them. To savour the nostalgic atmosphere of the old town, Avlaki with its fountains with the pure water from the Paliaskloupi spring, or to visit the old windmill. Town-Hall is housed in two neoclassical buildings and next to it is an authentic traditional coffeehouse, the "Lerian Club’ one of the few that have survived today.

Platanos and Ayia Marina, now indissolubly connected communities have the largest market on the island. It is a beautiful, small and hospitable town which has a lot to offer you, from its modern stores, where you can buy anything your heart desires, to the beguiling view from the fabulous Panayia Kastro. Built on top of Apityki hill, it stands commandingly above Ayia Marina, controlling the entire region with a panoramic view over the boundless blue Aegean Sea from Patmos to Kalymnos and beyond to the shores of Asia Minor. If you enjoy a romantic hike, you can reach it by ascending through the neighborhoods of Platanos going toward Ayia Paraskevi and from there you take the path with its approximately 500 stairs. For those in a hurry there is a comfortable automobile road. The Byzantine castle which was founded on the ruins of the ancient acropolis of Leros in the 7th century A .D. and completed during the time of Knights of St. John and the Venetians, is well- maintained. In its time it was impregnable with three ramparts and offered a sure refuge to the inhabitants during periods of hostile incursions.

The church of the Panayia stands out among the three small churches at Kastro; it lies on the west side and is the most important religious site the Lerians have. It has a iconostasis with gold inlays and icons worthy of note. There are many legends surrounding the icon of the Blessed Virgin of Kastro and the mystery of her power. In the Ecclesiastical Museum, which is housed in a new building next to the church, there are displays of rare manuscripts and holy books, precious icons, sacred vestments and other ecclesiastical articles. There are large underground storerooms and water cisterns at the castle.