Gastown
The Underbelly #1
Follow the path to its end (there will be some dead-end forks along the way). Eventually, you'll cross a walkway and spot this atop a table.
The Underbelly #2
Hope will let you into a new part of the underground after the Gastown Races. As you head through, take a right when you first encounter enemies. Follow this path, then head up the steps when you see the pipe pictured above to find the relic by a table.
The Bowels
You'll enter this area as part of "Chum's Holy Wrench," available from Chum after the Gastown Races. The area is very linear, so look for it as you move through.
The Dunes relics are on the next page!