You leave the locker untouched. If there is a puzzle here, it probably does not care whether you are dressed for it.
The concrete around the slab looks less random the longer you stare at it. Lines connect faint, carved arrows; the floor tiles form subtle paths pointing toward the heavy door.
You press your hand against the door. It sighs open, revealing a stone corridor that should not exist in a building with fluorescent lighting. Torches gutter in brackets along the walls, doing absolutely nothing about the health and safety situation.
On the wall beside you, three symbols are carved: a spiral, a straight arrow, and a jagged lightning bolt. Beneath them: PICK ONE, TRY NOT TO REGRET IT.