Notes on Terrains

Bug, Dark, Dragon, Fighting, Flying, Ghost, Poison and Steel are the only types without a Nature Power equivalent in Gen VII.

Flying, Dragon and Ghost had equivalents in Gen VI, which leaves Bug, Dark, Fighting, Poison and Steel with only types without an equivalent.

However, in Gen III, Secret Power used Bite's animation in caves.

Currently;

Fighting is associated with cliffs.

Bug is associated with forests.

Poison is associated with polluted areas.

Dark is associated with urban areas.

Steel is associated with buildings, which are currently associated with Tri Attack.

Though Dragon got Space, it is traditionally associated with caves and towers.