There are not only forests in fairy tales. Take the Snow Queen by H.C. Andersen, for instance. Lots of tundra. Don't forget the mermaid seas, the centaur plains and the Feydark, where everything is much muchier than in the Underdark. Every scent is stronger, every color is clearer, every feeling is intensified a hundredfold. The fair folk are quick to anger and quick to laugh.
Every fairy tale from every culture in the world might have been inspired by the lands of Faerie. Tir na nÓg, the Kakuriyo, Ljosalfheim, Wonderland, you name it - you could bring stuff in from everything.
In my campaign's Feywild, where the party is going at some point, they're going to meet a bunch of weird creatures, including:
- The Rabbit Prince, also known as El-Ahrairah or Inlérah, depending on his mood. Lord of all rabbits and hares, the Prince with a Thousand Enemies, and the Black Rabbit of Death. Stories of the puca are inspired by him - depending on his color, he brings either fortune or grief.
- Parsifal Nivens McTwisp, the Bane of Caerbannog, loyal knight of the Rabbit Prince, and worries too much about time.
- The Monkey King, Sun Wukong. Prophesied to go on a grand adventure in order to bring order to the world. Doesn't like order that much, so tries to avoid those mentioned in the prophecy.
- Sotlan of Summer, a cyclops pirate wearing an eyepatch because he was cursed by demonic fomorian magic to kill all that he lays his eyes upon.
- Chester, a fey feline of displacer beast heritage who turns invisible.
- The Erl-king, Wodan Winterbeard, former leader of the Wild Hunt. Stories of Odin, Santa and Harlequin are all inspired by him.
- The Green Knight, Nuadar Shavian, who once wielded the blade Claoimh Solais.
Good movies are Underground (Bowie), Legend (1985) and Strange Magic (2015).
Good reads are Dresden Files (every book has some amount of faerie as far as I recall, but it intensifies as the books progress) and A Midsummer Night's Dream.