Another good option for a long weekend is Antsirabe.
From Antananarivo, for Madagascar :-), an excellent road takes you in around 3.5 hours south to the third largest city in the country.
It features a thermal bath, historic buildings, the only car manufacturer (Karenjy), nice places to stay and eat well, omnipresent pousse-pousse (pulled rickshaws) and a rather cool climate to escape the heat.
It’s also known as the outdoor mecca of Madagascar, “famous” for paragliding, Mountain Biking and other outdoor activities.
If you want to know more, just let me know.