There is only one side mission available in the Downtown area and it is accessible after seeing the cut scene where the Nazis finish putting up the towers around the city. This is a guide for the last part I snagged from this website, very handy for anything Wolfenstein SP related. Just click side missions and you'll see this guide.
http://wikicheats.gametrailers.com/index.php/Wolfenstein_-_P...Radio Tower
Available when you watch the cutscene with the two Nazis working on the tower in the northeast section of Downtown.
Gold: 8
Intel: 4
Tomes: 1
Once you watch the aforementioned cutscene, speak to the resistance fighter marked on the map with a green ? to start the mission.
Kill the two Nazis working on the tower. The resistance fighter needs you to cover him while he sets a charge on the tower, so quickly get on one of the MG42 guns here and open fire and on the horde of Nazis that just swarmed the square.
Eventually, Rocket Troopers will enter the fray. Activate your Mire power when they arrive and be quick about gunning them out of the sky before going back to the earthbound Nazis. Switch between guns so that you're always manning one whose range can reach the main group of Nazis below. Listen for a female voice, signaling the arrival of an Elite Guard, and break away from gun to deal with her quickly. Once all the Nazis are dead, the charge will be set. Move away from the tower as it explodes.
You have two more ancillary towers to destroy Downtown. The first is a little east of the Black Market, so head there (ignore the star marker on your compass, which won't lead you here), and plant a dynamite charge on the tower. You'll earn $500 for blowing this tower up.
The next tower is in Downtown West, so go there now. This tower is guarded by a Heavy Trooper and several Nazis, so use Mire to deal with them. After you've finished them all off, blow up the tower for another $500.
One more tower to go, and it's in the Radio Station nearby. Enter it now.
Go through the double doors and you'll find several Nazis standing around and one on the balcony up and to the right. Trigger Mire and start gunning them down. Farther down the street you'll see three Veil-shielded MG42 nests; use Empower to destroy them. When this first area is clear, grab the Intel on the desk to the left, then move forward. When you get past the sandbags, check to the right of the car on the right side of the street for a bag of Gold ($100).
At the turn in the road, look left in Veil Sight to see a Veil ladder. Climb it and go through the door to find a box of Gold ($500). Drop back down to the ground now.
Move forward toward the museum to trigger the arrival of more Nazis and a Scribe. Trigger Mire to take care of them, then enter the museum. When you reach the room with the stairs on the left and the shielded door, look near the east wall for a bag of Gold ($100).
Head up the stairs to the second floor. Just before you reach the switch, grab the Tome of Power out of the busted glass case to the left. Pull the switch to shut off the Veil shield below. Several Nazis will rush through that doorway now, including an Elite Guard, so switch on Mire when you're ready to take them down. If you're quick you can get them before they even enter the room.
Go through the previously shielded doorway into the next area. The doorways into this room will be closed off with Veil shields when you enter, trapping you in with a Heavy Trooper, Scribe, and several Nazis. Trigger Mire and kill the deadly Scribe first, then the Heavy Trooper. Finish off the soldiers last. Use the columns to the right as cover; there's a Veil pool behind them.
When you're done here, exit the room via the hole the Heavy Trooper made in the wall. Hit the switch there to shut off the Veil shields. Leave the room and exit to the north. Grab the bag of Gold ($100) by the ventilation shaft, then crawl into the shaft. Take this route to its end, which puts you behind two Nazis. Melee the two of them, then turn on Veil Sight to see a Veil ladder on the wall. Jump up to the wooden platform on the crates, then climb the Veil ladder to the catwalk. Jump down to the lower ledge here to find a box of Gold ($250). Now return to the higher catwalk.
Crawl into the vent shaft here and take it to an office with Nazis in it. Gun them down, grab the Intel off the desk, then go east to the next hall. Kill the Nazis to the left, then grab the Gold ($100) to the right. Follow the hall to some stairs around an elevator shaft, which is guarded by a pair of Nazis. Make your way up to the next door, go through, grab the Intel off the wall, then go through the door to the roof.
Nazi snipers are watching this roof from the rooftop of the east building, so switch on Veil Sight and snipe them first with your Kar98. Once they're dealt with, go right around the corner to find some Gold ($100). Now move north. The stairs to the tower are blocked by a Veil shield. Follow the glowing blue power cable running to the shield to a room on the nearby building, below where the snipers were situated. Break out your Panzerschreck and fire a rocket into the room to destroy the Veil shield's power source.
Go back toward the tower and past the area where the shield was. More Nazis will attack here, so mow them down, then approach the AA turret to the north. Enter the room north of it to find some Intel on the wall, then return to the AA gun. Use it to destroy the tower. Several Rocket Troopers and Nazis will show up as you do this, so activate Mire and use the AA gun to take down the Rocket Troopers first. There is an alley in the corner opposite the big windows where you can hide and snipe Rocket Troopers. Watch out for the mortar shelling that begins at some point while you're fighting Rocket Troopers. It only hits in the area around the AA gun at the gun, the stairs, in front of the alley, and at the door to the room where the intel was.
Whenever everyone's dead, look around. You'll see that the exploding tower has created a new way down into the building via a gaping hole in the floor. Go through it and follow the path to the stairs around the elevator shaft, which incidentally is on fire. Run straight ahead past the fire and look left for a box of Gold ($250). Now run down through the building to the ground floor, then sprint to the exit doors to end the mission!