Down the Corridor

Wreathed in the glow of your Dancing Lights, you advance down the stone corridor, the soft click, click, click of your footfalls echoing around you.

After what seems an eternity of walking through darkness, you notice a tiny pinprick of green light emanating far in the distance. You take a beat to ensure all of your gear is in its proper place: travel pack strapped tight over your shoulders, spellbook at the ready, emergency hatchet hung by your hip. Finding everything in order, you quietly advance toward the dancing glow at the end of the hall. 

As you approach, a rhythmic sound grows louder, louder. The green light soon resolves into the magical, flickering firelight of an enchanted torch positioned in the corner of the hall, just before a northward turn. It casts no shadow. 

Once you reach the turning in the corridor, you realize you recognize the sound: what you are hearing is a regimented march, each of the steps exactly perfect. 

What do you do?