It reminded me both of Guell park in Barcelona and Hundertwasser Haus in Vienna. It is small - just around 1 hour there would do, but there are surprises there that I have not seen elsewhere. Ingenious structures. I liked it a lot and the kids loved it.
We made the route especially through there from Toscana to Rome. However I don't know if its so much worth the effort. If the other quicker road is boring for you... and if you have a spare 2 hours, then sure - go for it.

very beautiful , worth a visit specially if travelling with children they will sure love it , as we did

I have been trying to get to this garden since learning about the artisit, Niki de Saint Phalle, a few years ago and seeing her work in Paris. It was so worth the effort! If you are an art nouveau or Gaudi fan, you will fall in love with her use of color, images, and materials. Each of the 22 sculptures is unique and has a story of its own. We spent about 2 hours wandering through the garden, as well as going inside many of the sculptures themselves. This garden is worth a visit from either Rome or Florence; you can plan a stop at one of the beautiful beaches along the coast on the same day. But make a visit to this garden a top priority on your next visit to Italy!

This garden is at least as inventive and magical as the one that inspired it, Barcelona's Guell Park. It's a pity that it's a bit off the beaten track, or maybe it's fortunate because it makes it less assaulted by visitors as other places and helps preserve its innocence. Not all of its corners were accessible to visitors, though, which shows that it's suffered some wear and tear even as it is. It was otherwise also interesting to hear, talking to other visitors coming on the same day as us, that some of them had no idea that Niki de Saint Phalle and Jean Tinguely had been established artists, but were able to enjoy their work just as much. This is definitely a great experience for both children and adults and a great landmark of Modernism on the turf of Classicism, Renaissance and the Baroque.