It’s hard to define what exactly a castle is, so we’ll be including castle-like structures that happen to be called “fort” or even perhaps “citadel”. Surely all of them will satisfy some of your childhood hunger for a real-life fantasy–though their historicity might be a bit disappointing.
We’re beginning with this Czech castle, deemed largest by the Guinness Book of World Records at 720,000 (or so) square feet. It was originally built in the 9th century A.D. (with expansions through to the second half of the 18th century) and is currently the official office of the president of the Czech Republic. You can walk the corridors and gardens of this massive structure for free, or pay to see the many places within that are accessible to the public.
Although officially called a fort, this imposing Indian structure has the function and appearance of many a castle. Originally built in 1459 A.D., most of what stands today was built through the 17th century. It’s even bigger than the Prague Castle, at an insane 870,000 square feet. This fort might in this way be more impressive than any other castle, given the unity of the build. By the way: it’s free to enter, but worth a ticket to see the better attractions.
This castle is much larger than either of those other two, so long as you’re counting not only the structures but also the area enclosed by the massive outer walls. In this way we get a ridiculous measure of over 1.5 million square feet. This castle is located in northern central Poland, and housed the Teutonic knights for a few centuries back in the Late Middle Ages as a classic medieval fortress. And another thing: it’s made almost entirely of brick.
Hopefully these castles each appeal to you in their own peculiar ways. Who knows? Maybe someday you’ll go and see them yourself.