10 x 10
According to gaming legends, the name Dungeons & Dragons was just one in a large list of possible names considered by Gary Gygax when he was creating the game. After being asked, one of his daughters (he had three: Heidi, Cindy, and Elise) replied, “oh daddy, I like Dungeons & Dragons.” And thus the game was named.
This means there are two truly and necessarily iconic parts of D&D: you have your dungeons and you have your dragons. Both need to play a memorable role in the game. And yet they’re like Clark Kent and Superman: you rarely see the two of them together and when you do it’s usually forced and artificial.
By definition, dungeons are small, cramped, and unpleasant places underground. In contrast, dragons are typically large and prefer to fight above ground where they can make use of their wings. There are exceptions, such as dragon’s lairs, but even then you have to justify why a huge dragon has a lair with a labyrinth of medium-sized corridors accessible from the ground opposed to a hidden cave in the side of a vertical cliff face.