
Pula Arena
One of the world's best-preserved Roman amphitheatres.
Photo: Olgierd Rudak / CC BY-SA 4.0

A 3rd-century mosaic hidden in a sunken courtyard.
Photo: Ralfhesse / CC BY-SA 4.0
Tucked below street level behind an apartment block, this large 3rd-century Roman floor mosaic was uncovered by WWII bombing. Its central panel shows the punishment of Dirce, tied to a bull by the sons of Antiope: a scene from Greek myth, laid in tiny stone tesserae and free to admire through the railings at any hour.
It's behind the buildings off the main street and open-air: come any time, day or night, for free.
A small next-step selection from the same city.

One of the world's best-preserved Roman amphitheatres.
Photo: Olgierd Rudak / CC BY-SA 4.0

Tito's island paradise of dinosaurs and safari.
Photo: Wikimedia Commons / CC BY-SA 4.0

A cool maze of WWI tunnels beneath the city hill.
Photo: Psittacuso / CC BY-SA 4.0
Use the free map from home, then verify the discovery when you reach the place.