The last two school years we were involved in a very fun and frugal way of learning. One of our fellow homeschoolers organized a Learning Co-op that we could participate in. The rules were pretty simple: each family that wanted to be involved had to host at least one class (taught be the parent(s) or by a teacher they brought in) and then they could be involved in as many other classes that they chose to be as long as there was room. (We had to rank the classes we chose so that if a class ran out of room whoever ranked it the highest would get to go.) Each family could require a fee for the class they taught to cover material expenses.
I have heard of more complicated homeschool co-ops that cost a lot but I think this one worked wonderfully, the kids learned a lot and it was also a fun time to spend time with other families.One of the classes we had fun going to was on Nature Notebooking. We each brought our own notebook and colored pencils and then the teacher (a fellow homeschool mom) talked with the kids about the different ways we could observe (using all our senses) and also common sense rules for spending time in nature.
After visiting about it we went out and did it. We tried things like bark rubbing, drawing and attaching little pieces to our pages. Also writing down what we observed and looking things up on our flower guide. We had a good time.
Another class that I taught was on "Fun with Music" where we worked on rhythm and other basic theory through games and other fun activities.
I also had a lot of fun teaching a flower arranging class. (this one I did have to charge for to cover the cost of the flowers but they each brought their own containers.)
Some other classes we have enjoyed have been: