The St. Louis City Museum. Don't be fooled by it's name, this isn't much of a museum. It has almost 0 educational merit and is would be capable to house a Brotherhood base, raider hideout or a super mutant camp.
Busch Stadium. This is an amazing baseball stadium that could be used to house a massive amount of supplies, a slave camp, or even a small city (the field itself is bigger than Megaton and the stands could be used as a fortification and at the nosebleeds their could be snipers that could see for literally miles.
The Hilton. It could be a nice place to have housing in, similar to Tennpenny Towers.
The St. Louis Science Museum. Now this, unlike the City Museum, is an actual museum. It if full of scientific... stuff... that could be used in a number of ways such as their could be a weapon deep inside the museum, a Brotherhood mission to retrieve technology from a showroom, it could be a base for Enclave soldiers (who says it has to take place before Fallout 3?) and many more ways I'm sure the Bethesda team could think of.
East St. Louis. Ahh East St. Louis... the most crime ridden area in America... you know, maybe it would stay true to it's overly violent tendencies even after the apocalypse. This could be a huge city full of raiders raging war on each other for territory. This might not be a fantastic idea for the core game but maybe a good DLC.
The Missouri/Mississippi rivers. The Missouri and Mississippi rivers meet up together near the eastern borders of St. Louis (and no, not all of the eastern parts of St. Louis are 'East St. Louis' in the idea of it being dangerous and full of gangsters). This is what made St. Louis the big city it is today, way back when people used to travel the rivers on boats full of goods and would unload these goods at St. Louis. This would be an amazing place for a trading settlement because after an apocalypse traveling by water would be one of the most efficient ways possible.
The St. Louis Zoo. O.K. imagine a place full of mutated animals, all full of bloodlust and are jumping (or pouncing, rather) at a chance for some nice, tasty human flesh. Were would you go for that? That's right, you guessed it. The Zoo! This could not only house hundreds of mutated animals, it could also be home to some type of scientific laboratory where evil scientists preform cruel experiments with the FEV virus (yes I know the V in FEV stands for virus already).
Six Flags, St. Louis. This could be a really fun place to have a little bit of fun in. An amusemant park that is still partially operational after the nuclear winter. The possibilities are endless!
My last idea (for now) is also the most obvious of them. The St. Louis Arch. This is a famous monument standing over twice as tall as the Statue of Liberty holds great potential. It could have a secret prewar government base below it, it might just be a big base for a faction like the BoS or even just a super mutant camp. And, to top it off, you could snipe out of the windows in the top of the arch which stands well over 600 feet. You could pop the head off a centaur from a mile away!
Well guys, what do you think about the Cardinal Wasteland? Give some feedback below and if you have some ideas to add to this post leave them and I'll be sure to add it to the post and give you credit!