The map consists of a dark castle, as the name suggests. Bloons enter from the 4 left ground paths on the grass towards the 1 path castle drawbridge (which closes when the round ends and opens when the round begins). Towers may be placed anywhere along the 2 grassy fields, on top of the castle roof or, in the case of water towers, in the moat around the castle. However, the castle roof walls make the castle roof not ideal for towers affected by Line of Sight, especially Sniper Monkeys, so it's better to use the roof for Banana Farms, Benjamin, or other towers that ignore line of sight (you can also place small towers on the castle wall, which helps towers that shoot in a straight line). 30 trees on the left side of the map also block towers affected by Line of Sight (11 on the top, 6 in the middle and 14 on the bottom with half of 1 of them is offscreen). Each horde of trees can be chopped down for $1000 each.
- Main article: Dark Castle/Strategies
- In Version 6.0, the music for Dark Castle was changed from Sunset Samba to Tribes and Tribulations.
- This was the first Expert Map to be added to BTD6 in an update, Version 5.0.
- This was the only Expert Map in BTD6 that has one exit, until the release of Workshop in Version 12.0.
- The track's converging paths had confused the Elite Defender's attack speed algorithm on version 11.0, quadrupling its attack speed when targeting bloons before the paths meet. The glitch was shown off in this video. This glitch was patched on version 12.0.
- It is possible to beat Impoppable Dark Castle with only towers placed on the castle wall. This was done by ISAB on 7th (?) October 2019 and also here on 2nd of March, 2019 by 'Impoppable is Nothing'.
- This map seems to be the other half of the Snowy Castle map from Bloons TD Battles.
- Due to having a single path exit and large amount of space to place towers with less intrusive line of sight blockers, this map is often considered the easiest Expert map in the game.
- The flags on this map consist of a single banana on a red background, while Striker Jones' hat has a much more detailed design with leaves, darts, and bananas. The flag on Moon Landing is a banana on a blue background with circles around it. Admiral Brickell's hat consists of an anchor which is also the icon for Naval Tactics.
- After the balance changes to the Necromancer and Prince of Darkness in Version 21.0, there is a bug where the Necromancer's and Prince of Darkness's undead bloons always spawn on the start of the split lanes rather than further back along the track.