Green’s Dictionary of Slang

mare’s nest n.

[SE mare’s nest, a folly, an impossibility]

(N.Z.) a bar set aside for women and their escorts.

[NZ]N.Z. Observer 1 July 6: They could not help being brought into close personal contact with what some of them coarsely termed ‘the cats’ bar’ or ‘the mares’ nest’ [DNZE].