Do turtles sleep completely inside their shell?

Yes and no. Yes, because their shells are attached to their bodies(the shell is partly made up by the turtle's backbone), and if it were removed, the turtle would die. However, the turtles do not use their shells as shelter. There are several different habitats for turtles, depending on what type they are. For example, the snapping turtle and the painted turtle both like aquatic environments. The Box turtle likes a more dry environment, and the list goes on.