From Hurriyet Daily:
Two secret tunnels have been discovered under Turkey’s second largest castle, in the northern province of Tokat’s Niksar district. The tunnels date back to the Roman period, and it has been claimed that one of the tunnels was used by a Roman king’s daughters in order to go to the bath in the Çanakçi stream area.
The excavations are being carried out by the municipality in the 6.2 kilometer-wide Niksar Castle, which is Turkey’s second largest castle after Diyarbakır Castle. The tunnels are located in the southern and northern facades of the castle and are approximately 100 meters long.
read more here @ Hurriyet Daily