Other
National Museum of Women in the Arts: How to Make a Tunnel Book
Simple instructions on how to create your own tunnel book. These fun books create the illusion of depth and would be great for book report projects.
University of Cambridge
University of Cambridge: Nrich: More Christmas Boxes
Sharpen your logic and spatial reasoning skills while working on this challenge. Solution available.
Ducksters
Ducksters: Geography for Kids: Top 10 Lakes by Area and Depth
Students learn about the geography of the world's lakes and top 10 lakes listed by area size and depth on this website.
Wolfram Research
Wolfram Mathworld: General Solid Geometry
This page has links to general solid geometry topics, including depth, height, width, and length. A good introductory site into geometry.