The Amphitheatre of Serdica was an amphitheatre in the Ancient Roman city of Ulpia Serdica, now Sofia, the capital of Bulgaria. Discovered in 2004 and the subject of excavations in 2005 and 2006, the ruins of the amphitheatre lie on two adjacent sites in the centre of modern Sofia. The amphitheatre was built in the 3rd–4th century AD on top of a 2nd–3rd century theatre which had been ravaged by the Goths. However, the amphitheatre remained in use for less than a century and was abandoned by the 5th century.
It is a must-see because it is part of the ancient history of Sofia. The ampitheatre is well preserved in the basement of a hotel. You are able to walk around and enjoy the Roman past of Sofia.