"Well it probably cant lift the..." Jocasta began before a booming impact blasted dust from the seams of the coffin, lifting Beren and the stone lid like a hard footstep shifting a doorstop. Beren sprawled over the sarcophagus trying to hold it closed as three more blows rattled off the inside.
"Ok... well I can..." Jocasta said, pulling her hematallow from her pouch. A minor alteration of the spell would let her seal the lid to the coffin so that... CRUNCH. Dust exploded around a hole in the stone as the eldrich corpse within drove a fist through two inches of solid rock missing Beren by a few inches at most. The skeletal hand began to reach around, trying to find whatever or, in this case whomever, was impeding its well earned ritual murder rampage.
"Lets..." Jocasta began again. Beren nodded.
"Lets," he agreed. The both bolted. Beren hurdled off the top of the sarcophagus a moment before the lid exploded upwards like an over pressurised pot, flipping several times before it crashed to the ground and broke in half with a titanic crash. Jocasta was still staring as the corpse sat up in its mouldering funeral garb and began to climb free. Beren caught her and half shoved, half carried her down a side passage, through a series of decending archways.
"We don't need to be going down..." Jocasta tried to object as she managed to get her feet underher. The burst into another chamber much like the first. This one was in worse condition than the first. Gnarled roots of an unhealthy whitish color were in the process of prising appart the ancient stonework, their relentless assault having already tumbled masonry down to block one of the exits. They splashed through a pool of blackish water that was for sure filled with leeches and the gods knew what else.
"Flee now, cartography later," Beren suggested.