Each thematic expansion comes with its own bag of tiles, in addition to the other components (like pawns and objectives, as well as other special components that are specific to each expansion, like the Canal End tokens, more on those later).
When revealing Route tiles at the beginning of each round, players must follow a pre-determined mix of tiles from the Core Box bag and the Expansion bag. Each column will still contain as many tiles as the number of square icons at the top of that column, just like in a regular game with the core rules, so that the total amount of tiles available to players during a game will stay the same (which keeps the duration of the game similar to the core gameplay).
Even if the total number of tiles available during the game will be the same, it will be a mix of core and expansion tiles, though, which significantly alters the flow of the game and the availability of specific tiles during the game and creates new, interesting challenges. In the Canals Expansion, unsurprisingly, you will have to deal with the construction of Venice-inspired canals, bridges, and gondolas.
Your goal is to build Canals that are as long as possible (each Canal scores 1 Prestige point for each Canal tile it contains after the second tile, so a Canal with 5 tiles would be worth 3 points) and close as many of its open ends as possible (each is worth -2 points at the end of the game; to close a Canal, you just need to connect it to the Empty side of a tile, which allows you to place a Canal End token on top of it).
Additionally, some Canal tiles also have routes with open gaps over the canal itself where Bridges can be built when both ends of the "open" route are connected to other tiles. Bridges are very important to make points with gondolas (you want those romantic moments during your sightseeing tours), as each gondola is worth 1 point +1 for each bridge in the same canal.
