Another Castle is a Spell card introduced in Boss Monster: The Next Level.
This card works very similarly to a Kickstarter exclusive Spell, Agent of Evil, but it targets a Hero in the user's dungeon rather than a Hero in town. This card can be used for either sending a Hero that has been lured to your dungeon to another dungeon so as to deal a wound to an opponent. Or, it can even be used to send a Hero away to another dungeon that would have given the user a Wound.
The name of this Spell makes a reference to the end of each World in Super Mario Bros, where a Toad would be waiting for Mario to tell him the the Princess is in another castle. The artwork makes a reference to the throne room of King Toadstool seen in Super Mario Bros 3.
This card was amongst a few introduced in Boss Monster: The Next Level to try and replicate the effects of a few Kickstarter Exclusive cards in an attempt to keep with a promise The Brothers made to their original backers, while also giving people who missed the original Kickstarter a chance to play with cards similar to those Exclusive cards.