Judging by posts in the Solitaire Games On Your Table monthly lists on BGG, most 1PGers have been playing Carcassonne with the Carc Island solo variant rules. Now the game publisher, Hans Im Glück, announced their official solo rules (along with solo rules for another one of their games, Hadara), to help you pass the time if you are 'allein zu Haus'.
In this solo variant for Carcassonne, you first choose 3 different colours, and set aside four meeples of each colour. You also divide the tiles by three, and assign one third of them to each meeple colour. During gameplay, you will be placing tiles and meeples from each stack by going clockwise, eg. first the red meeple, then the blue, then the yellow, then red again and so on. Upon placing a tile, you have to place a meeple on it too, if possible. If there are multiple features that the meeple can stand on, you pick the one your prefer. You cannot place meeples as farmers.
If you run out of meeples of any one colour, the game ends and you proceed to scoring. Scoring only takes into account the meeple which is last on the scoreboard. The next time you play, you can try to beat your previous score.