Sand Sculpture Festival 2010, Blankenberge, Belgium

Tunnels large enough to enter are extremely hazardous; children have been killed when such underground chambers have collapsed under their own weight and instability, or due to the tide coming up or the structure being hit by a wave. Sometimes a dam can be built to hold back the water, or canals can be dug to contain the water.
Burying someone up to his/her neck in sand, or burying oneself, is another popular beach activity.