Castles of Mad King Ludwig: Colossal contains enlarged room tiles, tile trays with lids doubling as within-game tile holders, and a score track adjusted to the setup with the larger pieces (as they are not stored on the track in contrast to the standard game). The tiles are twice as big (i.e. four times bigger in area) compared to the standard tiles.
The expansion allows the Castles of Mad King Ludwig: Collector's edition to be played with larger pieces, especially convenient for solo play and conventions. For playing the game, the expansion requires the cards, card trays, and game pieces (player markers, coins, towers, tokens, etc.) of the base game.
The expansion contains a gameplay differences compared to the base game: The Foyer tiles (i.e. the starting tile for each player) of the base game have three entrances at both sides of the tiles. The Foyer tiles of the "Colossal" expansion have three entrances on one side and four entrances on the other side, thus allowing more variation in the starting position.
This expansion was available as a bundle with Castles of Mad King Ludwig: Royal Collector's Edition in the Kickstarter campaign.