No idea about the Gaelic mass but it would be a very quiet area to walk around on a Sunday morning depending on times as the city centre shops are only able to sell from 1pm on a Sunday so the centre is quiet before then. When I mean quiet I mean no one about which isn’t always a good thing. Having said that, if there is a Mass on and it’s summer then it would obviously be busier around the Chapel streets.

looks like it is a half mile/approx. 9 min walk. Here are the directions I copy/posted from google maps for walking directions. Hope it helps. it's a nice old church with lots of history and is in the center of town. Nice outdoor beergarten directly out the door, and down the lane from Castle st. mall Walk south-west on Talbot St towards Exchange St 0.1 mi Turn right onto Donegall St 151 ft Turn left onto Writer's Square 446 ft Turn left onto North St 30 ft Turn right onto Lower Garfield St 289 ft Turn left onto Royal Ave 141 ft Turn right towards Chapel Ln 62 ft Walk for 387 ft 387 ft Walk south 20 ft Turn right towards Chapel Ln 33 ft Turn left onto Chapel Ln