This level occupies the map slot MAP09. For other maps which occupy this slot, see Category:MAP09.
By using the switch behind the rocket launcher in the north of the "D"-shaped room with the large pool in the middle and the map exit (blocked by red bars) in the south, the bars in the east of that "D"-shaped room open up. Go through the door behind and strictly follow the walkway to its end. There is a patio behind a window to your west. Push the recess in the wall to the north to open up a small room (sector 719) with a berserk pack and a revenant on easy or an arch-vile on medium and hard skill levels.
In secret #1, first push the switch to lower a column in the "D"-shaped room, then enter the teleporter to get next to that (former) column, where another teleporter is on its top (- it is the eastern one in the pool). After using it, open the door in front of you to access a room (sector 440), containing two (on easy and medium) or four (on hard skill levels) rocket boxes and two (easy) or four (medium and hard) Energy cells.
After crossing the bridge raised by pushing the switch behind the red skull key, walk through the easy to miss vine-covered entrance at the western end of the walkway you just stepped on to enter a niche (sector 876) with three energy cells on easy and medium skills or, on hard skill levels, two cells and two rocket boxes.