there are three teleporter rooms on Plenitude

TIP!    teleporter room 1 contains 4 teleporters, 1 or more activate from the adjacent upper platform only ...  if not all turn on, the others will come on later
Teleporter 1 : Advanced Tomb!    TIP!   this is a great mission but 1 critical factor, KILL THE RATBOSS, the special trapdoor nearby then unlocks and that opens a whole new mission worth doing!! you'll love it
Teleporter 2 : Advanced Sewers   TIP!  this time the trapdoor pit in the middle IS OPEN and leads to a gorgeous lake (full of loot) 
Teleporter 3 : Advanced Castle   TIP!   easiest teleporter mission of the lot, teleport - find the path, grab the awesome loot, simple.  do this one if your team are low
Teleporter 4 : Advanced Dungeons TIP!   this is an Arena Battle revisited, have keys, bombs and a strong team
Teleporter 5 is hidden in Advanced (upper) Tomb and routes to Laboratory level (same as party can reach (initially) from Launch Beach!) [the trapdoors in Blue Stones are numbered the same way as Teleporter Room (But without the numbers)]Trapdoor 1 :  descend to Advanced Fetid Dungeons, tricky battle situation but look out for the NW stairs several minutes after the Unholy Horde appear, this is worth checking out Trapdoor 2 :  Tip grab the Blue crystal to descend to Mine Bridge, either stay on the bridge and exit via stairs to Upper Dungeon or drop off Bridge and hope you have better options on the Mine Floor TIP!   grab the rocks on the Bridge after you kill the Stone DemonsTrapdoor 3 :   Advanced Sewers MissionTrapdoor 4 :   Tip grab the green crystal to descend to Pontious Mission 1, INFO this can be heavy heavy stuff but a critical moment in the game TIP!  seek the floor plate in a Uguardian's cageTeleporter Room 2, 1 or more teleporters activate (some may not come on!)
Teleporter 6:   Petriefied Forest, the old ruins
Teleporter 7:   Laboratory I (Planetary experiment) Tip take Moon and Earth with you!
Teleporter 8:  Pyramid (Get the Master Key)
Teleporter 9:   Ruined Precincts :TIP take a Rapier with you
unusual locks
LOCK     LOCATION    LEVEL            COMMENTornate    South   Stin Dungeons      Fiery Etherals platformstatue  UPPER SECT  Zarchtod Tomb    trapdoor down from Stinking Dungeons "Big Hall" in centrePROGRESS?Q   I'm stuck at the end of Fetid Dungeons   A   see Routes , no 1 "Night Forest with trapdoor down to Blue Stones"  go back to a previous save if necessary , get to North Tomb Level or Stinking Dungeons Big Hall (trapdoor down to Upper Tomb) Q   Castle Level has no way out,  A , slay the 2nd Skeleton Commander OR can you get to THE BEACH?  remember the POND has a trapdoor down, did you explore down from there?? OR see answer above (for  I'm stuck at the end of Fetid Dungeons)