Going to an abandoned warehouse
It appeared as though the dog was reacting to something out of the blue. Mark was being pulled in the direction of a massive, abandoned structure when the animal began to bark and pull as hard as it could on its leash. It seems to have been used for storage at one point in time, but it was deserted and unused now.
A peak in the basement
Meg was fixated on something that was happening inside of the building, and it was capturing her attention. As they made their way to a small window just above the ground, Mark could feel his heart pounding in his chest. Meg had ended up tugging him there. Mark most likely chose to go down into the basement after getting a glimpse of what was going on down there.