I believe they actually built that…
Also, there was meant to be an Eiffel Tower in London. They got as far as the first storey (I believe) but ran out of money and dismantled it, and built Wembley Stadium instead.
Another vote for the second Taj Mahal, too. My eyes nearly fell out of my head when I visited it. Another one, symmetrically opposite, in black marble, would have made my balls drop off.
I’ll third the Taj Mahal. As I recall, the black-marbled one was meant to be the tomb for Shah Jahan himself, so he could be placed right aross the river from his wife. The current Taj Mahal is fantastic; if the second one was built, well, fuck me. 
Or the LaGrange space colony they promised me in about 1969!
jjimm: there’s another visionary structure that won’t be built in Tokyo, it’s called X-Seed 4000.
You guessed it, four-thousand meters high. Not exactly Frank Lloyd Wright’s mile high one, but close enough 
Hmmm… residents of the top floors of X-Seed 4000 would probably get altitude sickness. The article says: “This is the tallest building ever envisioned”
I say bullshit, because I just envisioned one that’s 4,001 metres high! So there!
Dare I say it: publicity stunt.
Oh, so I’m expected to READ the OP all of a sudden? The rules in this place for us noobs are harsh 
Ok, so I’m a :wally
You registered in April 2000 and you’re a noob? What does that make me then…?