Inside the Fortress are lots of goodies:
First, the statues of Superman's parents, Jor-El and Lara, holding up the globe of Krypton. The statues are on raised platforms toward the back of the Fortress. This is a feature of the Fortress not present in the movies, but only in the comics. I opted to include it anyway because it seemed so fitting with the Man of Steel's character - the Fortress is a monument not only to a long perished, powerful civilization, but in Superman's eyes it is also a reminder of who he is, and the very reason he is alive today. The statues are a reminder of Supe's humbleness, and his striving to uphold the example his parents set. Plus, they just plain look cool.
And okay, I confess: the globe here is actually not LEGO, but a painted wood piece. However, to get the right look I cheated on this one element, as I know the LEGO group has produced spheres.
Second, the molecule chamber from "Superman II". It harnesses the red rays of the Kryptonian sun and... well, if you have seen the movie, you know (and I'm guessing most of us have, but for the rare person who hasn't, I won't spoil it and will instead suggest you check it out!). The front of it comes off and a minifigure easily fits inside. I arranged for a transparent floor, and a lever at the back of the Fortress will change the floor tiles underneath from white to red. Of course, a red light brick would really work best in this instance, though.
Third, the crystal control panel. I wanted the look of something solid but clearly made of ice or crystal, just like the movies. And I quickly lost count of the number of clear 1x1 plates, 1x1 rounds, 1x1x2/3 tiles, and other related bricks it took to build this! The clear whip aerials really help add the look of the crystals as well.
Fourth, the control panel also has a clear floor and unlike the molecule chamber, I was able to light it up. A light brick would be handy here too, but in this build I used a very small LED flashlight, which can be slid under the floor of the Fortress.