Victory Road is a system of caves and outside areas where you will fight trainers and find quite a few items.
Pokémon that you can catch here
New pokémon that you can get here are Heatmor, Durant, and Deino.
Getting through Victory Road
First, go into the cave entrance that you reach after passing through the Badge Check Gates.
Next, if you have Surf, go north and across the water for a Max Revive. Then go back across and up the stairs.
You will encounter Ace Trainer Shanta who has an L45 Whimsicott and Zebstrika.
Exit through the door south of Ace Trainer Shanta. Outside, after you walk toward the right, a Veteran and an Ace Trainer will talk to you. The Veteran will slide down the side of the mountain, but the Ace Trainer will be too scared.
Go to the east and slide down the wall from the gap in the fence. Then continue east and head into the cave (there isn't anything of interest beyond the cave entrance here.)
Surf across the northern water to get a Rare Candy. Then go up the stairs.
Don't bother with the southern exit because it will just take you back to where you were. Instead, go north and up the stairs there.
Ace Trainer Dwayne is here with an L45 Stoutland and Scolipede.
Go outside after defeating Dwayne, and you can head east if want TM12 Taunt, but you will have to slide down in order to get it, which will put you back at the beginning of Victory Road.
Otherwise go left. The first cave entrance takes you to Veteran Tiffany, who has an L44 Beheeyem and Heatmor as well as an L45 Lilligant.
Now if you head east and down the stairs you can push the boulder with Strength to give yourself a shortcut. Then go back and head north, going up the stairs to fight Ace Trainer Cathy who has an L44 Simisage, Simisear, and Simipour. There is a Full Restore nearby.
Now go back to that outside area where the Ace Trainer was afraid to slide down the wall, and go into the cave entrance on the left. You'll encounter Black Belt Tyrone who has an L43 Scrafty, Mienfoo, and Conkeldurr.
Now you can go up the stairs, where Doctor Logan is waiting with an L43 Gothorita and Leavanny. He will heal up your pokémon afterward.
Head north from the doctor and there is a Strength boulder that you can push, as well as a hidden Revive. Go up the stairs. Don't go through the southern exit unless you need to backtrack. You should instead go north in order to proceed.
Up the stairs you'll find Ace Trainer David, who has an L44 Klang, Seismitoad, and Darmanitan. Go out through the left exit for a Full Heal, then go back and through the exit on the right.
Slide down through the rightmost gap in the fence, then go through the cave entrance here. You'll find Veteran Martell in here. He has an L45 Gigalith and an L46 Eelektross. Go north and up some stairs to the next floor.
If you caught Cobalion in Mistralton Cave, then you can go down the stairs in this room and push the boulder out of the way to reach a cave where Terrakion awaits.
Otherwise, go outside. There is a Pokémon Ranger here who just talks to you. If you wish, you can slide down through the gap to the right of the Ranger, which gives you a way to get a Nugget, hidden Max Revive and Max Potion, and TM02 Dragon Claw. If you go back and slide down to the left of the Ranger, you can get to an area with TM93 Wild Charge, as well as access to other hidden items.
If you head north from the Ranger, you will reach the Pokémon League.