This crypt has been in use since pre-Christian times. It’s a huge, eerie, natural cavern where the echo of leaking water drip-drips. Originally a place of pagan worship, it became the home of the martyr Restituta in the 5th century and a reference point for Cagliari’s early Christians. The Orthodox Christians then took it over – you can still see remnants of their frescoes – until the 13th century, when it was abandoned.
In WWII the crypt was used as an air-raid shelter, a task it wasn’t up to, since many died while holed up here in February 1943. It’s interesting to make out the wartime graffiti that covers the walls.