Half-Life 2 Walkthrough -> Follow Freeman!
In the square in front of the former museum building, there are several locations with grenade launcher shells needed to kill the Striders. These are the same huge, three-legged mechanical enemies, one of which you saw near the very beginning of the game.
The first ammo spot is in a bunker right in the center of the square. To get there, you'll have to go forward, drop down into the pit, cross the pipe, and climb up the slope to the left of the pipe. From the bunker, shoot down all the striders you can. The second ammo spot is right next to the building opposite the former museum. Now head back to where you first entered this square, to the soldiers. After killing them all, descend the stairs underground to the familiar path.
So, near the house, we turn left and enter through the hole in the wall. The building itself is a multi-story parking garage. Three soldiers are behind the doorway ahead, so you can throw a grenade or a barrel in there without delay.
We move carefully but quickly toward the first staircase. There's a chest with ammo there. From there, we shoot down the strider, after which we return our squad. Behind the chest is a lambda sign. We replenish our ammo and continue through the hole in the floor.
Beyond the hole in the wall, a rebel will tell you that the street is full of striders, but if you find higher ground, you can shoot them down.
We go outside and see that something truly terrifying is going on. An entire block, maybe more, has been razed to the ground. We enter the underground parking lot (in a white minibus, with a lambda sign under the right brake light and armor inside) and turn right, back outside, toward the strider.
We run past him and jump down. Don't linger here—an explosion will soon ring out, and part of the floor will collapse. We run back outside, down the slope. If the squad is already gone, several rebels should appear here.
We move forward, past the soldiers, into the small, still-standing room, and climb up one floor. We pass the crates and jump down to the level below. This place is a dead end, at least for now. We need to wait for the strider to blow up the far wall, creating a passage for us.
We conclude our participation in the street wars by killing the remaining soldiers. Near the horse on the pole, we meet Barney and Dog, who has killed more than one enemy and broken more than one wall in search of his mistress. Under the barrier, Dog finds a passage to the citadel and waits for us to enter.
Well, there are no other options anyway. Let's jump. End of Chapter Twelve. Our Benefactors are next.