Schwartz's is a landmark in Montreal (the other being the poutine at La Banquise) and is the reason why the city is famous for its smoked meat sandwiches.
As you may have noticed from the photos, the sandwiches are basically 90% meat and 10% bread. It takes skill and training to be able to eat the sandwich while keeping it intact. The meat is oh-so tender and, in the true Quebecois fashion, is grease through and through. The mustard also blends well with the grease.
On any given day you'll see a mix of tourists and locals lining up in front of Schwartz's for a bite of the delicious meat. The wait is normally around 30 minutes, but you can shorten that wait to 15 minutes if you get takeout instead (at the takeout shop right next door).