There is a little bar in a plaza near La Bicicleta– a cafe I was a regular at– se llama Las Vacaciones.
This place has a glorious Sunday brunch and a variety of mojitos (like a coffee one, that as gross as mint coffee may sound is delish). But the real real: that brunch has bomb options and their tapas are always so, so good.
A great place to drink when it’s not late enough for Madrileños to really be “out” yet for the evening (read: before 11pm).
This bar seems to have more girls drinking here than any other place I kicked it, and I think that the female owners of this place may feed into that– like maybe its a known femme space in the city? I don’t know for sure, but the frequency of it being a girls-only crowd was odd for, what seemed to me, a highly male city.
Vacaciones is the place one of my dearest friends in Spain first told me about the experiments he did in his internship and my love of the word “chiquitin” was solidified**. It’s a great place to get close to people (literally, its tiny) and as bright as it is, and as happy as the decor is the mood just sets you off in a whirl of good energy.

There were always a hodge podge of visitors to the city and locals, so be prepared for the typical Spanish stares, but also maybe drunk Australians.
Here’s the place’s website: http://www.vacacionesbar.com/
**Chiquitin: a typically Castillian (i.e. not Spanish-speaking America) word meaning “very small.” Like “chiquito,” which you’ve probably heard.