The Kennedy School in the Alberta Arts district is definitely a must see. Opened in 1915, later abandoned and taken over by the McMenamins Group, it has been beautifully restored and its hallways are covered in incredible artwork.
The school is huge, with sprawling wings in which you can find a theatre, a soaking pool, a restaurant with a beautiful courtyard, as well as lots of guest rooms.
You can easily wander around the premises just to check it out (I also recommend the Alberta Arts district just around the corner while you're in the area), but if you do stop in for a bite to eat the food and service is fantastic as well.
For lunch my husband had a burger and salad, and I had a African peanut rice bowl: both were excellent, as is the beer there.