The Fortress can be visited
Marmaris Castle

Marmaris Fortress, a structure on the Turkish Aegean coast, rises above the town of the same name. It once served as a military base. Today, it houses a museum.
History+
The origins of Marmaris Fortress date back a long time; it is estimated that a fortification was built on this site as early as 5000 years ago. The historian Herodotus reports on city walls in Marmaris that are said to have been built around 3000 BC. A reconstruction took place under Sultan Süleyman the Magnificent, who used the fortress as a military base during his campaign against Rhodes.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://en.wikipedia.org/wiki/File:Marmaris_Castle.jpg
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 36.8507, 28.2744