Dr. Abawuwu's Fortune Apparatus
Select Dr. Abawuwu in the game menu or click on the top-right X to be taken to city overview, then click on the covered wagon:
You can use Dr. Abawuwu's Fortune Apparatus once a day and spin the wheel. You can test your luck up to 20 times a day by spending a mushroom each or 10 lucky coins. Lucky coins are rewarded for watching the flying tube's ad clips.
You can win experience points, gold, wood, stone (in two different amounts) and also items (even epic ones if you are lucky!) and mushrooms.
All resources won before level 25 (you need a level of 25 to build the fortress) are saved for later use.