I encountered these interesting puzzles while hiking in the Marjan. They are made entirely of recycled materials and dead trees, and therefore cost nothing to build except a bit of labor. Essentially, they challenge the user to kinetically (i.e., by manipulating chains / one’s own body) calculate elements of the fundamental group of different shapes. It was amazing to see such a great example of public math education and engagement through puzzles in parks, especially in one as beautiful and historic as the Marjan! I have been in contact with the artist(who, sadly, is not a mathematician), and have received her permission to adapt the puzzles. I am hoping to find a broader community to engage in this sort of work and perhaps construct similar puzzles in the Southern New England area. If you are interested in this sort of thing, please get in touch with me!
Topological Puzzles in the Marjan