The script called for a magical puddle so the set was raised from the studio floor. The puppeteer operated from underneath, laid on a trolley.
Being a multicam shoot with the set raised off the floor, the walls were trucked for access. So the ceiling sections were supported by the corner towers, the back sections of which were also on castors.
The cauldron puppet was shot through a trap in the chimney. Most specially built furniture had camera traps.