The mausoleum is a small stone building inside the medieval ruin garden, built in 1938 to mark the 900th anniversary of King Stephen I's death. It is a stark, intentionally austere design — clean classical lines, no ornament — built directly above the spot where the king is thought to have been buried in the original basilica.
The interior holds a few of the most important surviving pieces from the destroyed royal church, including the lid of a sarcophagus believed to be King Stephen's own. The site is treated as a national memorial and an annual coronation-mass commemoration is held here on 20 August.