Experimenters Dylan and Phoebe visit Nina to find out why people use arches in buildings.
Triangles
Pointy Roofs
Piers
Nests
Houses
Windmills
Beaver Dams
Skyscrapers
Bridges
Demolition
Floating Houses
Rollercoasters
Arches
Lighthouses
Living Underground
Living Underwater
Igloos
Spiders' Webs
Domes
Amphitheatres