Palazzo Castellania, the law courts building of the Knights, will be open for visitors on Saturday night as part of Notte Bianca.
Particular attractions are its first floor hall and the underground cells, where Mikiel Anton Vassalli was held as a prisoner.
The palace, in Marchants' Street, was built in 1760 and continued to house the law courts until 1853. It was later used as a school and as government offices.
In 1905 Sir Themistocle Zammit made his groundbreaking discovery on undulating fever in his small laboratory at the top of the building. That lab has been preserved and will also be open for visitors.
The building now houses the Department of Health.