Stuck in Prince sarovet’s cave

Help! I am stuck, really! I cast the Mark spell at cave entrance and then went to the place where walls suddenly fall around you. I panicked and cast Recall to get out. But now I can’t return to that place anymore, and some guides tell me that I would need to get a key from there! How to reset the cave walls to original status? I can’t go anywhere except the fishing village now!!

If you search around to the south of the wall that closed, you'll find a secret switch that will open that wall.