Reaching the Funicular
Regardless of how you get down a level, make sure that you end up on the second floor. If you came through the elevator shaft and vents, then you're there already. If you're in the lobby, just look to go up the steps to an overlooking spot. There's a very nice armory behind a keypad on this level, hack it if you can.
The main objective is to get past the TV studio full of soldiers. There is a turret on the main floor, three guards by the desks, two on top and one heavy that likes to patrol the whole area. Get on the second level and use some takedowns to knock out the two men on top. There's a sniper rifle up here with a few boxes of bullets. I strongly suggest that you grab it. It'll come in very handy in a little bit, and you should have room for it.
If you aren't committed to a stealth run, I suggest that you use the sniper rifle to pick off a few of them. You should aim for the heavy first. A headshot will still kill him. If you want to stay quiet, look around for the “ogre" class mercenary. If he's walking up the ramp, wait for him and ambush him. Otherwise, go down the steps and use a desk for cover to pick off the first patrol. Swing to the left and stun the second. The third should be by himself still, so move between a few more desks and bring him down. Look to get behind the heavy on his patrol and you can wrap this all up.
Once the area is clear, use the desks for cover to keep the turret from seeing you and head out to the locked door. You can either hack the keypad and use the ramp to get down, or break through the wall and come out a vent. It honestly doesn't matter much.
There are two guards walking together here. If you have the reflex booster augmentation, you should easily be able to sneak up behind them and knock them both out. A stun gun and takedown combo will work too at close range. Once they're down, you're free to explore. There isn't much of note though.
The real objective is the Funicular. Don't go through the main marked door. It's too easy to be spotted. Go to the left and look for the open side entrance. If you have the strength augmentation, you can pull the nearby vending machine out and use the vent to get behind the security terminal for the turret. You can also slip through the open side door and use the pillars to avoid the two patrols, or pick them off with a stun gun. There's a vent in the back wall under the stairs that will take you under the floor and past the turret too.
Regardless of how you do it, you can sneak over to the security terminal behind the turret and shut the turret down if you can, or reverse its codes to make it fire on the mercenaries.