Portals are marked on the map, with their opening order. Repeat the process while looting a chest on your way (after portal P3), until you reach another chest at the end (after P4). Each pressure plate activates a portal, so step on the only one available and go through the newly opened portal. You will reach an area with pressure plates and portals. Take the other path and go down the stairs. You will reach a fork, so proceed ahead and turn right for the power symbol (R2) (secret 3/14).

Use the lantern filler again, and continue on the main path and go through the secret wall shown the map (SW) (secret 2/14). Use it and return to the starting tile for a recipe (R1) (secret 1/14). Continue until you reach the lantern filler. Use the lever to unlock the door and grab the chest behind it. Follow the path until you reach a 'roundabout'.