From your third dig on, the tunnel is roped off until you choose your route. A survey stand by the arch offers two ways down to the same artifact, each with its own ground, and the rougher one pays 50% more kudos if you bring the artifact home. Bring home the Surveyor's Scarab and it maps both routes, showing what lies where before you choose. Press E at the stand, then hold 1 or 2 to take a route; the rope comes down for the one you pick.