The Lower Plant is the last dungeon of the Subterranean Canals. Most of the enemies players have run into before are encountered. On the first visit, you will see Vincent observing the main characters, commenting about not underestimating them again.
This is also the first dungeon to feature a sub-boss, the Elite Haken, which the player must take on two of at once. The main boss of the Lower Plant is the Lobster King.