Chapter 15's Cosmic Realm is a mind-bending location that sends you round in circles, which makes finding all of the City of Ry'uul secrets a bit of a pain. Though far from the largest level in Doom: The Dark Ages, its several separate maps make it hard to figure out exactly when you're able to access secrets you can see just out of reach.
Don't worry though, I've figured out the perfect route to collect all the Doom: The Dark Ages secrets in Chapter 15, City of Ry'uul, so you're not clueless in the Cosmic Realm. Below you'll find all the secrets and collectibles laid out in chronological order, so you can easily grab them as you go through the mission.
