I was about to comment this! Although the both the cathedral and garden seem larger, the Palais idéal has very intricate details, somewhat reminiscent of the Sagrada Família. All built by a single man, ferrying stones on a wheelbarrow.

There was a recent movie (https://www.imdb.com/title/tt7248884/) about the man and his creation, I quite liked it.

More picture on the French Wikipedia palace page: https://fr.wikipedia.org/wiki/Palais_id%C3%A9al