Starkbierfest literally means "Strong beer festival" and it it held in Munich every year during lent. The word strong is referring to the wort content, the thickness, of the beer not to the alcohol content, although there is a fair degree of correlation there which makes for a typical starkbier to have 18% wort and 7.5-7.8% alcohol. We're talking a thick dark lager beer with a kick.
All the breweries in the region produce a starkbier, but the real festival is held in two locations: the original at Paulaner Am Nockherberg and the rival at the Löwenbräu Keller.
This second biggest starkbier celebration in town is at the Löwenbräu flagship beer hall's fest hall. The atmosphere is very similar to the Oktoberfest, but with a distinctly "locals only" flavor as quite simply most tourists don't know it is going and don't know how to get there.