Great atmosphere, relic of "old" Toronto, good draught beers.
I've been coming here for years with my dad/uncle/cousins/brother/grandfather when looking for a dark upstairs cavern to enjoy some early afternoon brews (while also scarfing down the delicious hot veal sandwiches from San Francesco's next door, which you're allowed to do).
Apparently, based on stories from my dad and uncle who used to frequent the Monarch back in the 70s and 80s, it used to be a "no-ladies gentlemen's club" where all sorts of pranks and shenanigans between beers went down. In it's present manifestation, the environment is much more tame (though smug patriarchy still oozes through the walls), while the furniture, mostly well-worn leather, dinged hardwoods, and scuffed felt, give the aura of times past. It's a decent sports bar with a few tvs, a pool table, and tons of hockey memorabilia hanging from the wall (things like autographed Bobby Orr photos, etc). Beers are no longer 25 cents a mug, as legend had it, but you can still get an ice cold Boddington's or Keith's for an average price.