This is the first area. Called "Outer Ring". So far there are 2 types of secrets in this area.

Secrets in this area always look like this:

A secret hidden room behind a sandfall. You don´t need anything to access it. Just walk through it.



The other type of secret is this red wall. You need an explosive urn to access it. You can see this urn on the screenshot. Unfortunately you can´t access it with the burning lantern so you really need the explosive urn to access it. (this is also the only entrance to a secret room which needs an item)



This is how the wall looks like after its destroyed:



This wall can also look like this: (which is a little bit harder to notice)

This is the second area. Called "Gardens of Remorse". So far there are 2 types of secrets in this area.

Secrets in this area always look like this:

A secret hidden room behind these plants. You just need to jump to access it.



Thats basically the same like above but its much higher on the wall.



You need to use your whip (with RMB) at that ring to access it. (Tip: hold "Space" to access it much easier and climb up the edge)

This is the third area. Called "Catacombs". So far there are 2 types of secrets in this area.

Secrets in this area always look like this:

A secret hidden room behind this wall. You need to crouch or slide to access it. Just press "C".



A secret hidden room behind these rocks which you need to destroy with an explosvie.

This is the fourth area. Called "Palace Grounds". So far there are 2 types of secrets in this area.

Secrets in this area always look like this:

A secret hidden room behind this hole in the wall. You need to crouch or slide to access it. Just press "C".



A secret hidden room behind this wall where you need to jump over (press Space) and crouch through the second wall (press C)



The window can also be red:



From a higher perspective you can see the entrance much easier.

This is how these secret hidden rooms look like from inside. There are always no enemys inside. (Forget it. I found my first enemy who spawned inside of it:)



So far I´ve also never encountered any cursed treasure. Please let me know if you have! ;-)



(There is also one more tip. You can´t find these secret rooms inside of buildings. They are always in larger areas outside of buildings. Thats very obvious to notice but maybe its helpful for you)