To unlock the Big Tunnel achievement in Big Walk, first open the tunnel network through the yellow tower key puzzle, then walk into one of the large tunnel entrances.
Big Tunnel is easy to miss because the entrance is tied to a larger island unlock, not a random cave you can walk into at the start. Once the yellow tower route is finished, the large tunnel gates become usable and the achievement should pop as you cross into the underground network.
What Big Tunnel actually wants
The Big Tunnel achievement is for entering the unlocked underground tunnel system in Big Walk. It is not for riding the train, using the chairlift, or passing through a small passage that only looks like a tunnel.
KEY!
Think of it as a late traversal unlock: the big entrances stay closed until the yellow tower key work is done, then the island’s tunnel network opens up as a walkable fast-travel route.
Requirements before a big tunnel opens
| Requirement | What |
|---|---|
| Yellow tower objectives | Complete the power nodes, book blocks, relics, and related yellow tower tasks. |
| Puzzle rewards or MacGuffins | Bring the required rewards to the console at the top of the yellow tower. |
| Tunnel key | Use the console to create the key for the tunnel system. |
| Key cutting | Start at the key cutter near the bottom of the yellow tower, then follow the pillar markers to each cutter until the key is finished. |
| Mountain tunnel lock | Insert the finished key at the large yellow tunnel on the mountain to open tunnel entrances across the island. |
KEY!
Before you can enter a big tunnel, you need to finish the yellow tower chain. That means clearing the tower objectives, turning in the required puzzle rewards at the tower console, making the key, cutting it through the key cutters, and using it at the large yellow tunnel on the mountain.
The exact number of required MacGuffins is the only fuzzy part: early route notes mention five, while other player guidance just calls them the required puzzle rewards. In either case, bring the needed red egg-like rewards to the yellow tower console and follow the key sequence from there.
Bring a flashlight before entering, because the tunnel corridors are extremely dark once you step inside.
How to enter the tunnel system in Big Walk
Once the yellow tower key work is finished, use the large tunnel entrance near the yellow tower area and walk inside.
STEP 1/5
Find the yellow tower area
Open the map and look toward the yellow lighthouse-like challenge tower near the top-left side of the island map.
STEP 2/5
Check that the tower objectives are done
The tunnel gates open after the required power nodes, book blocks, relics, and key/podium unlock chain are complete.
STEP 3/5
Approach the opened tunnel entrance
Go to the large yellow tunnel structure on the hillside after the finished key has opened the tunnel network.
STEP 4/5
Walk through the big tunnel
Cross into the tunnel entrance to trigger the Big Tunnel achievement.
STEP 5/5
Use the underground hub
Follow the corridor to the hub signs, which point toward the different challenge tower routes.
Video help
What the tunnel network does
After you enter, the tunnels work as a fast-travel network between tower and challenge areas. The underground hub uses directional signs, so you can pick the corridor that points toward the part of the island you want instead of making the whole trip overland.
The system is still something you walk through yourself. It shortcuts travel, but it is separate from the train and chairlift routes.
Mistakes that keep Big Tunnel locked
| Mistake | Fix |
|---|---|
| Trying big tunnel entrances too early | Finish the yellow tower objectives and key sequence first. |
| Using the train or chairlift instead | Walk into a large unlocked tunnel entrance yourself. |
| Checking the red hub before the network opens | Return after the yellow tower key has opened the island tunnels. |
| Entering without a flashlight | Carry a flashlight so you can see the dark corridor and keep moving. |
If the achievement is not popping, the problem is usually that the tunnel network has not actually been opened yet. The big hub opening and the mountain tunnel only become useful after the yellow tower key sequence has been completed.
Goals after tunnel access
Once the tunnel system is open, it also helps with other traversal cleanup. You can move between challenge tower areas faster while working toward route-based goals like Big Ride for the train, Big Sit for the chairlift, Big View for the map, and Big Wall for going beyond the wall.
The same access also puts you on the path toward the shiny studio deep in the tunnels for Big Makeover. Use the tunnel entrance near the big red hub and follow the color-coded corridors when you are ready to chase that next objective.
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