After you complete Kiawe's trial in Wela Volcano Park, you can proceed to Route 8.
Open the Barricade
Go to Route 7 and go north to approach the Captain's Barricade. There will be a cutscene, and afterward you can access Poké Pelago by pressing X and choosing it in the menu. Read the Poké Pelago page for more details.
After the cutscene, go north to the Trial Guide in front of the barricade on Route 7. She will open it for you. Go north to enter the tunnel.
Dividing Peak Tunnel
Go north through the tunnel. After a cutscene, go north to reach Route 8.
Go north to find a fishing spot in the water. There is also a hidden Max Repel nearby.
Go back to the street and go west. If you have a Passimian, you can show it to the father and son.
Go west and enter the white building. One of the Aether Foundation members will ask you to catch a Goomy, then show her your Pokédex. Goomy can be found in Lush Jungle.
Talk to the other girl, and if you have a Big Malasada with you, you can feed it to the Vulpix. The girl will ask you to come back tomorrow. The next time you come back, you can offer to protect the Vulpix while it plays outside. The next time you visit, the Aether Foundation employee will take Vulpix to the snowy mountain that it loves.
Leave the building and go west on the street. In a cutscene, you will get TM43 Flame Charge.
There is a Poké Finder spot under the Aether Foundation building.
Go north through the grass the Aether Foundation building to find a path that goes northeast behind the building. You can battle Backpacker Kiana at the end of this path. She has a level 20 Eevee. You get 480 Pokédollars for winning.
Near the backpacker, there is a Big Pearl.
Go back to the main road. Go west and you can battle Rising Star Mikey. He has a level 20 Phantump and a level 21 Trumbeak. You get 1008 Pokédollars for winning.
To the south of Mikey, there is some grass, and you can find a Miracle Seed there.
Just west of Mikey, there is a Hyper Potion.
Farther west, there is a hidden Adrenaline Orb.
West of that, you can battle Rising Star Nicki. She has a level 21 Stufful. You get 1008 Pokédollars for winning.
To the left of Nicki, you can go into the grass and go northeast to get an Ultra Ball.
South of there, you can battle Scientist Tyrone. He has a level 20 Amaura and a level 20 Omanyte. You get 960 Pokédollars for winning.
South of the scientist, there is a path to the Fossil Restoration Center. There is a hidden Awakening to the right of the trailer. There is a Rare Bone behind the trailer.
You can't do anything more at the Fossil Restoration Center right now, so just go back to Route 7.
Go west from the Fossil Restoration Center and you can find a hidden Iron behind the rock.
Go south from there to find Hau, who mentions Festival Plaza.
In the nearby Pokémon Center, a Backpacker asks to trade your Trumbeak for her Arbok.
Outside, you can go west and talk to the boy to battle Preschooler Kaleb. He has a level 19 Kangaskhan. You get 228 Pokédollars for winning. After the battle, you get a berry.
Keep going west to find the Roadside Motel. Go around the left side of the motel to find a Dive Ball.
Near the Dive Ball, you can battle Golfer Alan. He has a level 20 Hoothoot. You get 1200 Pokédollars for winning.
In the middle of the parking lot, you can battle Golfer Maile, who has a level 20 Natu. You get 1200 Pokédollars for winning.
Go southeast from the motel's front office to find a dirt road. Go along the southwest path of this dirt road to go down to a rocky area where a Wimpod is walking around. If you try to go up to it, it will run into its den. If it goes into its den, go into the Pokémon Center and come back out. The Wimpod will be outside again. If you get into the water with Lapras, you can go around to the den and prevent Wimpod from running away.
While you go through the water, go southwest to find a Water Stone underwater.
Go north from there to a small island where you can fight Karate Family Samuel and Guy. They have a level 21 Machop and a level 19 Machop. You get 900 Pokédollars for winning.
Get into the water north of the island, then go northeast to the area with Wimpod's den. Approach it and it will try to run away, but it can't reach its den, so you can touch it to have a battle with it and try to catch it. However, be warned that Wimpod can use its Wimp Out ability to escape the battle if its health drops below 1/2. Be sure to keep its health above 1/2. Mean Look and Spider Web do not stop Wimpod from escaping with Wimp Out. If Wimpod runs away, you have to wait a day for Wimpod to reappear in the area. It only appears during the day, not at night.
If you have defeated all trainers in Route 8, you can talk to the Ace Trainer to the left of the Aether Foundation building to battle Ace Trainer Eileen, who has a level 23 Fletchinder and a level 23 Fearow. Her Fearow is holding a Flynium Z. You get 1564 Pokédollars for winning. Afterward, she gives you TM58 Sky Drop.
If you are ready, go east to reach the northern part of Route 5, which you couldn't reach earlier.
Northern Route 5
Before going through the captain's barricade to reach Lush Jungle, you can go south from the gate to explore the north part of Route 5.
Southeast from the captain's barricade, there is a hidden PP Up on a rock.
Go south from there and jump down the one-way ledge. There are a couple of dens to the left that pokémon might come out of. There is a hidden Nugget in front of the left den.
To the west of the dens, you can battle Preschooler Caleb, who has a level 20 Charjabug. You get 400 Pokédollars for winning.
Go west, then north through some grass. If you go east from there, you can battle Hiker Gabriel. He has a level 21 Makuhita and a level 21 Mudbray. You get 672 Pokédollars for winning.
If you go up the ramp east of the Hiker and keep going east, you will find a Full Heal.
You can go southwest from there along a narrow path to find TM59 Brutal Swing.
Go back the way you came and go west past the Hiker. Keep going west to find Ace Trainer Alexis. She has a level 22 Goomy and a level 23 Sylveon. You get 1564 Pokédollars for winning.
South of the Ace Trainer, there is a Hyper Potion.
Go to Lush Jungle
There is nothing else to explore in this area, so when you are ready, stop at the Route 8 Pokémon Center to heal up, then go south, then east, to reach the gate to Lush Jungle.