The official Ubisoft forums (and the older German forums) have sections dedicated to fan content. This is the birthplace of many legendary scenarios. The German community (where the game is wildly popular) is particularly active; don't hesitate to use a browser translator to browse their "User Created Content" boards, as they produce some of the most technically complex scripts in the world.
The definitive archive for Anno 1404 content. It hosts hundreds of user-made scenarios ranging from peaceful building challenges to intense military conquests. Nexus Mods Anno 1404 Player Scenarios Download
Installing a downloaded scenario is a simple process of "drag and drop." The exact folder depends on whether you are playing the original game or the Venice expansion. Player Scenario - Custom map :: Anno 1404 - Steam Community The official Ubisoft forums (and the older German
Do not put files in the Program Files folder. Go to: C:\Users\[YourUserName]\Documents\Anno 1404\Savegames The definitive archive for Anno 1404 content
To save you from downloading 500 broken maps, here are the five highest-rated custom scenarios that still function perfectly.
: A long-standing German community site that houses an extensive database of scenarios, mods, and maps. Note that while the site is in German, many scenarios are compatible with the English version of the game.