Ha ha, that can happen. I love Monty Python too!! One problem with living over a waterfall is that the water gradually will erode the rock your castle was built on, nibbling away at your foundation so your fortress falls in the water bit by bit... O.o Niagra falls has moved back by quite some distance over the time humans have been visiting it, for example. Kind of ruins the idea, cool as it is.
Admanantium, really? Guess my Galactic Imperial Mining Survey Ship is in luck!! *activates tractor beam and drags entire adamantium rock right out of the landscape and into space* YEEHAW!! This will fetch 7.8 million quatloos per ton on the imperial market for sure- yay for spaceship hulls strengthened with admantium. *everyone in the castle suffocates in vacuum* Mark a claim on this planet for mining rights, will you, yeoman? What do you mean, inhabited? Well, they must be primitive... forget it, the Sagittarius Accords only apply to planets with a Class 5 culture at the very least. Get the load secured and prepare for the jump home, we've gotta move before Dickinson tries to get his claws into this... literally. First starship into a system with adamantium, this will make us rich!!