Different doors may prevent you from continuing your path. They have to be unlocked in different ways.
These doors can be opened with switches. Some switches can open and close doors whenever wanted, other switches can only temporarily open doors.
These switches open and close doors whenever you pull them.
This switch will temporarily open a door, you will need to hurry.
These doors can only be opened with stone pressure pads. You need to stand on them, have a monster stand on them or drop a stone or explosive crate on it.
This pressure pad already has a stone on it, thus keeping the door opened.