The transition to the first room in the tower is a small blue square at the end of a corridor.
When we went there, there were mobs above, which the auto-warning script told us were there, asking for a confirmation to transition.
But it was very, very hard to get up to the next area with that warning. Because the transition is floor based, you cannot click it, like you normally can.
Eventually, but running onto and off the square really quickly, I could get up, but then I was up there fighting the whole room with the others still trapped below.