A Giant Fish Tank
Wouldn't it be cool to make a great big fish tank surrounded perhaps by modern buildings filled with aquariums.
It came along quite nicely at first. An underground cave assessible via a passage, and an embedded shipwreck.Then I discovered a lot of things like furniture and plants can't be placed/planted in water. And of course the fishes in JJX are invisible unless you catch them first and put them in fish tanks, and fish tanks can't be placed in water.... I thought I could surround the glass tanks with blocks but then the darkness generated monsters in front of the fish tanks. It just couldn't work out nicely.
I'll revisit the idea again someday, maybe make it not so big.