The Tırmıl Ruins can be found in the Tırmıl factory complex in the Akdeniz İlçe on the eastern side of Mersin. Surrounded by factories and warehouses, seeing the remains of this ancient structure peaking through the mound can be a bit surprising!
These ruins are dated back to the chalcolithic age, though their exact time period is not known. Among the many stones surrounding this mound, many pieces of pottery and artifacts have been, and continue to be, found. If you pay attention, you may find some yourself (though taking them is illegal according to Turkish law)!
Of the remaining structure of the castle atop the mound, only two bastions remain. As to the history and importance of this castle, not much is known for sure, though some evidence from ancient texts indicate that this may be Kale-i Hebelleç.
From the top of the mound, there are great views of the whole of Mersin.
This site is easy to access from both the Mersin-Adana Road (D400) or the Serbest Bölge exit from the Otoban (151 Cd.).
Some steep hiking is necessary to reach to the top of the mound (which is not very tall), but if you walk to the south side of the hill and follow the goat paths, you should not have too much trouble.
See the map below for directions. I would recommend parking on the north side of the mound and walking around to the south side before ascending the hill.
This location is a good stop on the way from Mersin to Tarsus, or on the way to Kazanlı to see the birthing place of the sea turtles.