The Cehennemagzi Caves are three caves side by side in the Ereğli District of Zonguldak. The former name of the area was Acheron Valley. The first cave consists of two parts. The first part of the floor is paved with original floral and geometric motif mosaics, and the apse and stairs in the second part mean that this area was used or arranged as a church in the early periods of Christianity. The second cave is located next to the first and is known by the locals as Koca Yusuf Cave. Currently, only 350 m2 of the 1.5 km is visible. The third one is the largest and is probably used as a cistern. It is believed that the legendary hero Heracles traveled to the Underworld to finish his 12th mission from the Cehennemagzi Caves.
