Supra Bailly is an institution in the Chatelain area. It is right on Rue de Bailli and is open at all times.
While the setting in quite shabby and unintentionally retro, Supra Bailly is popular with people of all ages and from all backgrounds. The beer is extremely cheap (starting from 1.50 euro for a small beer), the service is very fast and the staff is friendly .
While it is not a lesbian cafe/bar, many lesbians tend to go there for drinks.
Very strongly recommended. One of my favourite places in Brussels.