Lava

Lava is a type of space in Bloons Adventure Time TD that only characters that can withstand the heat can be placed on. Lava cosmetically appears on tracks in other Bloons TD games, but it is equivalent to unplaceable land there, with the exception of the Portable Lava Lake, a Trophy Store skin for the Portable Lake in Bloons TD 6.

Maps with lava
The following two maps contain lava, both contained within the Fire Kingdom:
 * Lava Pools
 * Flame Kitchen

Placing towers on lava
Two characters, Flame Princess and Ice King, innately have the ability to stand on lava without any trinkets. Lady Rainicorn allows other towers to stand on where lava was as well.

Other characters must equip specific Trinkets to be able to be placed on lava.
 * The Jetpack allows any character to float over the lava.
 * Blazing Feet, Red Cowboy Boots, and the Candy Dive Suit allow any character to stand on lava.
 * Iron Hull allows Captain Cassie and Commander Cassie to float on lava.