I rarely have peope around to play Carcassonne and Brettspielewelt is less than ideal for me. So, out of boredom, I invented solitaire rules for Carcassonne. It plays nothing like the real game, and it isn't particularly fun. It is, however, a challenge.
The object is to build a city within a city while scoring large amounts of points. Remove the starting tile. Shuffle all your pieces together. It really helps to use all the expansion pieces, except for the river. Draw a random tile to start. Continue drawing random tiles and placing them as you would in normal Carcassonne. Try to build a small city and then surrround it in an unbroken ring of cities. The ring of cities may be joined at the corner of the pieces, but may not have open sides (I wish I could illustrate this with pictures). Continue until all pieces are placed.
Scoring is as follows:
-The surrounded city is worth 3 points per tile and pennant
-Each completed city in the completed ring is worth 2 points per tile and pennant
-Each completed city outside the ring is worth 1 point per tile
-Roads and cloisters inside the ring are worth 3 points per tile
-Roads and cloisters outside the cities are worth one point per tile
-Incomplete roads, cloisters, and cities are worth nothing
-If the ring is not completed cities are not scored at all