Having the mind set of a five year old, I thought id jump straight into the stupid end of the pool with this the p1500 ratte by Krupp. For those unfamiliar it was a proposed super tank weighing in at 1500 tons carrying 2 800mm main guns, several 128mm secondary guns and a selection of 20 and 30 mm flak guns for self defense. It was to be powered by either 2x8000hp man ship engines or 8x2000hp MAN u-boat engines. By anybodies standards this thing was as big as a ship and probably would have pushed materials technology beyond even the Nazis abilities, but god you'd have papped your self if something twice the height of a maus super tank came rumbling over the hill.
As far as real tanks go, Ive always had a soft spot for the Swedish s-tank. Designed as a defensive tank to stop the pessky russkies from rolling into IKEA land, it had a fixed 105mm gun with an auto loader and to aim it the whole hull was tilted up or down on adjustable suspension or turned left or right on its tracks but it had a total height nearly half that of a conventional tank allowing a very low profile when dug in. Also those vertical grills along the front of the hull are a Swedish version of Kremlin Armour designed to stop AT missiles.
Ive resisted the temptation to put a pick of my volvo up as a tank.