Environment Book Series
The Environment series were a series of splatbooks for Dungeons & Dragons 3rd Edition that focused on different types of environment.
Frostburn
Frostburn focuses on taiga and tundra environments as well as supernaturally cold planes. On the crunch side, it adds a bunch of ice themed abilities.
Mechanically it is notorious for introducing the Shivering Touch spell, which does 3d6 (~10.5) points of dexterity damage that stacks with itself for a third level spell. This spell is absolutely bonkers since enemies rarely have that high a dexterity score, and even ones that do will rarely survive multiple hits from it.
Sandscape
Sandscape focuses on badlands, desert, and wastelands. Unlike Frostburn, there's not that much fire or extraplanar material.
Stormwrack
Stormwrack is your oceanic splat, with new sea monsters, aquatic/amphibious races, sailing ship rules, etc.
Cityscape
Cityscape is all about designing cities and running urban adventures.
Dungeonscape
Dungeonscape is advice to building better dungeons.