Its floor is a frozen lake of clear ice with a surface area of about 2,000 square metres (22,000 sq ft).

To the left of the chamber an opening leads into the Salle Maude at the base of a 20 metres (66 ft) ice-wall called Niagara.

Casteret's original survey shows the passage extending for a further 100 metres (330 ft), but this is no longer accessible.

[8] The ice in the Grande Salle is ponded and has formed as the result of cold air flowing through the system, with areas out of the draught being water.

In 1950 the entry into Salle Maude was a low crawl across the ice floor about 30 centimetres (12 in) high.