18. The Hollowed-Out Giant Oak Terrarium
Instead of building a traditional metallic or stone dome frame, the Hollowed-Out Giant Oak Terrarium uses nature itself as the primary building block. The exterior resembles an impossibly huge oak tree, but the center of the tree trunk and upper canopy have been hollowed out and replaced with a seamless dome of tinted green and clear glass. Inside the hollow trunk, a complete self-contained ecosystem thrives. Vines trail down from the living wooden walls, while a winding spiral staircase carved directly into the heartwood leads players up through various forest layers. Butterflies fly within the hollow heart of the tree, surrounded by living wood and filtered sunlight.