The Roman Amphitheatre can be visited
Roman Amphitheatre Augusta Treverorum (Treves)

The Roman Amphitheater in Trier, completed around 100 AD, offered space for 18,000 spectators and served as a venue for gladiatorial contests, animal hunts, and public executions. A unique feature was its dual function as the eastern city gate of Augusta Treverorum.
History+
Erected around 100 AD, the amphitheater quickly became an integral part of the Roman city of Trier. It was a place of entertainment where local dignitaries and imperial officials, sometimes even the emperors themselves, offered the populace "bread and circuses." Animal hunts and gladiatorial contests were commonplace, and executions also took place here. Unusually for an amphitheater, it was integrated into the Roman city wall, simultaneously serving as the eastern city gate. This use continued until the 5th century. After the fall of the Western Roman Empire in the 5th century, the structure, like many other Roman buildings in Trier, was used as a quarry during the Middle Ages.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 49.7480, 6.6491