Several of these Hidden Treasures normally require mobility perks (triple jump, springs, jet pack to help jump higher or ninja to crawl up a wall) but all are possible without, although some are easier than others.
Note that in most of these videos you can see that the glitch is active by the mid-air running animation; this was removed in an update and you should watch instead for the different leg position
Browse through the entire list, or go directly to
Campaign
World 1 - Angel Room
Used to require mobility perks or glitch jump, but they refreshed the world in 2.3.2 and now you can do a double jump:
World 2 - Angel Room
No perks needed
World 3 - Angel Room
No perks needed
World 4 - Angel Room
No perks needed
World 5 - Angel Room
This needs Dwarf (previously some heroes could enter without). You can either double jump from the bottom;
Or drop in from the top:
World 6 - Angel Room
No perks needed (don’t push the ice-block; go up and around)
World 7 - Starting Room
This used to require dwarf to go down a crevice but 1.14 changed the location
World 7 - Angel Room
Dwarf required.
World 8 - Angel Room
This used to require mobility perks or glitch jumping; but 1.14 introduced a little ledge to make it easier
World 9 - Angel Rooms
The first one doesn’t need any perks:
The second usually needs mobility perks; but you can jump on to the edge of the slope and jump off again, and then if you see the leg moving animation (and maybe sometimes even if you do not) you can do another double jump:
My 6 year-old figured out another way to do it - run against the last step and jump, and then quickly turn back… I’ve only tried it a few times but the leg moving animation has always appeared, which makes this a bit more reliable (but if you don’t get it right you will go through the portal!)
I’ve noticed that if you have springs the above either don’t work or are hard to trigger, so you can try this alternate strategy:
BTW if you have Ninja (very useful in this world) you can go up from the side:
World 10 - Angel Rooms
The first one doesn’t need any perks:
For this one, you need to jump over the Stop sign (if you walk, you will press a hidden switch and the access will be blocked - if that happens you can walk back to open it and then jump over) and then use the trick explained for the Poison Castle if you don’t have mobility perks:
Alternately, it also works to jump while running against the step (I’ve found the previous method works better but YMMV):
World 11 - Angel Rooms
No perks needed
No perks needed
World 12 - Starting Room
No perks needed; walk under the falling blocks and the last one will operate the switch
World 13 - Angel Room
Tiny required
World 14 - Angel Room
No perks required
World 15 - Angel Room
No perks required
Daily Elemental events
Metal Monday - Starting Room
No perks needed
Toxic Tuesday - Angel Room
No perks needed
Winter Wednesday - Angel Room
No perks needed (the ice gives you a boost)
Thermal Thursday - Starting Room
No perks needed
Fey Friday - Starting Room
Tiny required
Weekend Boss Fight - Starting Room
No perks needed
Castles
Metal Castle - Starting Room
No perks needed. Don’t push the top crate too far or you won’t be able to move around it.
Or if you like doing the glitch jump, you can try this:
Metal Castle - Angel Rooms
Dwarf required:
This one normally needs mobility perks. The trick is to not jump off the 2nd window (move off, let the hero move across a bit and then jump) - falling off the 3rd window isn’t required 
Poison Castle - Starting Room
No perks needed
Poison Castle - Angel Rooms
This one doesn’t need any perks, just jump on to the invisible platform:
This also doesn’t need perks, but sometimes the jump doesn’t succeed and you fall down - so it’s good to try this when the upper mine is moving left (like it is in this video) so you don’t hit it when you fall there
This one is the toughest: You need to jump up near the block, then when you fall back to the level of the block, run against it while jumping - you need to get the timing of that just right and also maneuver into the crevice to double jump:
Another option (video from Raúl Fernández on FB, I haven’t been able to replicate it) is like this:
Looking at it frame by frame, it looks like jumping while running into the block sometimes gives a jump that is higher than the regular jump (and then you still need to maneuver into the crevice to double jump like above)
Ice Castle - Starting Room
No perks needed
Ice Castle - Angel Rooms
This one doesn’t need perks, but you will take damage unless you have Safety Bubble (or perhaps Titan Shield - I’ve noticed in the poison castle that the mines don’t hurt you if you have it?). If you think the reward is worth 1,000 health points, do it fast so you only get hurt once:
This one usually needs mobility perks:
Fire Castle - Angel Rooms
This one doesn’t need perks (need to move just a little to the left as you jump)
This one normally needs mobility perks (can probably be done from the other side as well)
Magic Castle - Starting Room
No perks needed, just go down the vine
Magic Castle - Angel Rooms
No perks needed for this one, double jump off the top of the vine while going left and keep jumping
This one is easier with dwarf:
If you don’t, you can go from the sides but it is tricky to do it without getting hurt from the spikes when going in and out (it is possible but haven’t got a recording)
Magic Castle - Last Boss Room
This is the only secret chest in a room with enemies AFAIK. Need to track down the recording to upload, but it’s easy to find - once you kill the boss, keep going past the portal. There’s a chasm that you need to jump across (don’t worry if you fall in, you reappear from the top). And then there’s a small “chest” that you need to jump up on
Dark Castle - Starting Room
All the regular castle secret treasures apply in the Dark Castle as well (including the Magic Castle last boss if you get it). Additionally, there was one in a starting room, I’m not sure if this has been removed or it requires Tiny:
Gun Dungeons
Monday (Auto Handgun) - Angel Room
This one didn’t require Tiny, was updated to require it, but has now reverted to being accessible without Tiny
Tuesday (Plasma) - Angel Room
No perks needed. Note that this Gun Dungeon is a bit unusual in that there are 3 Angel Room layouts and you only get 2 on any given run - so on some runs you will not get this room
Space - Angel Room
No perks needed
Wasteland - Angel Room
No perks needed
