To find hidden spaces without the Scope Sight item, just shoot the Rebound Gun (4) at the walls, straight up. If it disappears for a bit and bounces back to you, then there's a secret cave. PS: Sorry for so much comments :P
@ShadowWyvern, I still use the Legionnaires an Genies on lvl 4, and when the Sandworm comes, just change the rally point to get out of the attack zone.
Again, in level 23 (Third level of Gluttony section), it also shows the wrong demons. That's the only flaw of this game, but other than that, amazing game, 5/5.
Also, in level 19 (Third level of Lust section), instead of having the Soul-Stealer Demon, it has the Burglar Demon instead, though it shows the Soul-Stealer Demon.
In level 15 (Third level in Wrath section.), It doesn't say that the Fast Demon (Tall blue one, introduced in level 3 in Sloth section.) will be in the level, yet near the end the Fast Demon does come. Please fix that.