地下墓穴, or "underground tombs," are burial sites located beneath the ground. These structures are often carved into rock or built with bricks and stones. They serve as final resting places for the deceased and can be found in various cultures around the world, including ancient Egypt and China. These tombs are designed to protect the remains from natural elements and grave robbers. Many underground tombs are adorned with intricate carvings, paintings, and artifacts that reflect the beliefs and customs of the people who built them. They provide valuable insights into historical practices surrounding death and burial.