"Some monsters occupy multiple beds. When you need more beds, upgrade the castle."
The Castle is a Structure that allows for Monsters to be placed on an Island - each castle provides a certain number of beds for monsters. Aside from Gold Island, each island starts with the same Basic Castle and the progression through the castles is the same, with the same number of beds for each level of castle (the number of beds per castle is increased on Ethereal Island, due to the fact that Ethereal Monsters occupy large numbers of beds), but the time and cost required and Experience granted for each upgrade differs based on the island. Gold Island has a single castle - the Crystal Castle - which does not have a bed limit, and cannot be upgraded.
There are two mini-games that you can play from the Castle; you can learn more about them by clicking on the links below:
The Castle produces a bass sound. However, it cannot be heard until you have at least a Modest Castle.
In the following table, the number of beds shown is given as the number on all islands except Ethereal, followed by a slash and the number of beds on Ethereal Island.
"Singing takes a lot of energy, and monsters need sleep! The Basic Castle really isn't very comfy at all; the rain gets through, it's drafty, and cramped."
"It's great to have a good night's sleep! The Modest Castle is dry and warm, but small."
"Ah, some elbow room! The Comfortable Castle even has indoor plumbing."
"The Spacious Castle has lots of room for monsters to relax and refresh."
"It just doesn't get any better than this! The Luxurious Castle has everything a monster might enjoy, from cold slime pools to dark, nasty dungeons. Who would ever want to leave?"
"This state of the art domicile goes way overboard when it comes to spoiling the monsters... Personal assistants to wait on them hand and foot (at least those that have hands and feet), the spiffiest sound systems on the monster market... They've got it made in the shade."
"After agreeing that more beds equals more fun, the monsters set out to create the most capacious castle ever - and what better inspiration than Gold Island's own Crystal Castle? Following extensive study of the original architectural marvel, the multiverse's finest architects were tapped to craft the new castle in its image. After the smoke cleared, there was no question - this is the be-all and end-all of monster living arrangements. Welcome to paradise!"
When first introduced, the Extravagant Castle had a maximum of 52 beds. However with the update to version 1.1.3, the maximum beds was increased to 60.
The Vita version of the game currently does not include the Paradise Castle. However, the PC version does.
For a long time, there was a hint of a new castle being added. The hint could be viewed from the log-on screen hints and tips. It said, "The Extravagant Castle is the Maximum Castle. For now." This hint has now been realized in the Paradise Castle.
"Although shaped like a castle, this mysterious structure actually serves as the main power generator in the monster dimension of the multiverse! It's from here that monsters derive their musical inspiration, as well as their tireless energy so that they can keep singing forever!"