Terraforming Mars: Big Box is both a storage option for all the Terraforming Mars material released to date — the base game, five expansions, and the first-player rover — and a set of 3D terrain tiles to dress up the game. Included in the box are:

24 city tiles (four each of six designs)
40 forest tiles (eight each of five designs)
9 ocean tiles
14 special tiles (the original eleven, plus three new ones)
Terraforming Mars: Big Box also includes three new cards that relate to the three new special tiles, card dividers, and five plastic markers for the global parameters.