The seven gates lead to the same world that Tirta had previously traversed. Everything points to L-02 at the end of L-03; actually, it's quite easy to get there on a normal day, though they still can't reach the castle at L-02 without permission from the Queen. However, because this was the recruitment period for Candrasa's men, they had changed their route to L-02 through the gates in L-03.
They wouldn't be able to get to L-02 through anywhere but the seven-gate passage. All areas above and below the gate have been marked; they have everything under control. The only safe area on L-03 now is in the Hanging Gardens, where they have come and been rounded up.
Because once they enter the gate, they will not be able to get out again. The choice is to go inside the walls and win or be killed.
