MAP18: Optional Bases Opposed (BTSX-E2)

MAP18: Optional Bases Opposed is the eighteenth map of the second episode of Back to Saturn X. It was designed by Paul DeBruyne (skillsaw) and uses the music track "Birdsong," composed by Stuart Rynn (stewboy).

Essentials
The keys in this level may be collected in any order. To exit, it is only necessary to collect the blue key and either the yellow or red keys.

Take the megaarmor and shotgun, which are protected by imps and a Hell knight and/or chaingunner, then go outside and head north-west until you reach an area with two slime pools and some shotgun shells. Go inside the east building and dispose of two mancubi that are revealed ahead, then go up the stairs and turn left at the top to see steps leading down to a switch. Drop to ground level and look south-east to see that a platform with chaingunners (and revenants on Hurt Me Plenty skill level or higher) has lowered to reveal another switch, then pull that switch to open a door behind you concealing another revenant. Drop down the hole behind this door to a corridor with imps, spectres and zombies, then head east to an outdoor area where an arachnotron protects a supercharge and a small switch; the switch will open a door to the south concealing an arch-vile, but will also open monster closets with imps to your left and right. Go through the door you just opened and follow the hallway to a lift, activate it and kill a revenant then ride the lift up to the yellow skull key.

Follow the passage back to the starting point, then go outside again and head south towards a ledge with one or two arachnotrons on it - there is a doorway opposite this ledge that you need to pass through. Go down some steps to an archway overlooked by a knight and mancubus, then go through the archway to an enclosure with imps, demons and revenants. Look behind the green brick pillar for a doorway and walk through it, go up some steps to your right then turn left at the top and walk forward until you see the wall ahead lower, revealing a chamber with more of the same opposition. Continue following the path north and east to a switch, which will raise some platforms across the center of the enclosure, then run across those platforms to the east ledge and kill two imps and a zombieman (or two cacodemons and a chaingunner on Ultra-Violence (UV) and Nightmare (NM)) that are released in front of you. Head north to a ring-shaped hallway that leads to the arachnotron ledge you saw earlier, then turn right to reach a walkway and follow it round to an arrow button that lowers a nearby lift. Ride the lift down and step on the red floorplate in the enclosure, which will open a door in the north wall but will release imps, demons, cacodemons and revenant into the area. Ride the lift back up and go through the door you just opened to get the red skull key.

Go back to the starting point and head due west to a pyramid, which contains the exit teleporter, then go round it and continue west past an arachnotron to a brick doorway. Turn left and go forward until you drop into a winding path, which you should follow until you see the walls around you lower; quickly head back the way you came at this point, as two arch-viles have been released from compartments at the north end of the path. Pull the switch inside the east compartment, then head to the south-west corner where some bars have lowered to reveal a staircase leading up. Drop off the top of the stairs and push past some imps and cacodemons to your right, then cross the bridge to a marble tower and use the lift on its west side to go up to the blue skull key. Taking the key will lower a barrier to the north and allow you to reach a lift - ride that lift up and kill the mancubi, shotgun guys and revenants waiting ahead, then follow the walkway east and south past a door to a switch. The switch will open the door you just passed, so go through and head back to the pyramid where some knights and a spiderdemon will teleport in; climb to the top of the pyramid and open the colored bars at the top, then step on the red pad to finish the level.

Official

 * 1) South-west from the start, near a pool of slime with two dead marines and the chainsaw, there is a ring-shaped structure where a supercharge is visible in the center (sector 562) through a small window. Press on the nearby green torch to lower a wall leading to it.
 * 2) At the north-eastern part of the map is an elevated section of the level, where a supercharge is visible on a pedestal. Near the stairs to that section is a square shutter. Press on it to open a small compartment (sector 96) containing a berserk pack.
 * 3) Ascend the stairs from secret #2 to find the supercharge with a computer nearby. Press on the computer screen to lower the pedestal (sector 140), allowing access to the supercharge.
 * 4) On the north-central part of the map, a button can be pressed to lower a rocket launcher, and which also lowers some walls containing monsters. On one of the closets that opens next to the rocket launcher, there is a hidden crucifix button. Shoot that button to reveal a teleporter on another of the monster closets nearby, allowing you to telefrag two barons of Hell (arch-viles on UV and NM) in the beginning area and eventually access a fenced off courtyard (sector 787) guarded by two arch-viles (on UV and NM), containing a supercharge, shotgun shells and armor bonuses.
 * 5) On the eastern-most part of the map, shortly before finishing the path that ultimately leads to the red key, there is a desert-like area surrounded by blue torches where you are ambushed by teleporting monsters. You can use three small pilars on that area to climb to a small section containing a tiny hole. Falling down that hole leads to a small underground secret area (sector 509) containing a supercharge, two boxes of rockets and a medikit.

Non-official
On the western part of the map, at the start of the route leading to the blue key, there is a section with a zig-zag shaped path which ultimately lowers to reveal two arch-viles and a button unlocking a plasma gun and allowing to proceed further down the path. That same button also opens the bars to another section to the west which requires either the red or the yellow key and contains a BFG9000. Beware the revenants that teleport in around you when you approach the BFG.

Current records
The records for the map at the Doom Speed Demo Archive are:

The (absence of) data was last verified in its entirety on February 21, 2022.

Player spawns
This level contains seven spawn points:
 * 1) facing north-east. (thing 35)
 * 2) facing north-east. (thing 570)
 * 3) facing west. (thing 571)
 * 4) facing south. (thing 572)
 * 5) facing north. (thing 573)
 * 6) facing west. (thing 574)
 * 7) facing east. (thing 575)

Things
This level contains the following numbers of things per skill level: