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Big Walk Big Tunnel Achievement: Enter a Big Tunnel

Open the underground tunnel network through the Yellow route, then walk into one of the network’s own entrances. Opening it is not the achievement trigger.

Big Tunnel is attached to the tunnel network the Yellow route opens. The trigger is entering one of its tunnel zones, not placing the key or opening the gates.

Achievement
Big Tunnel
Official requirement
Enter a big tunnel
Verified trigger
Enter a tunnel entrance zone
Requires
Tunnel network open
Not the same as
Riding through a railway tunnel

Where are you stuck?Open Tunnels Guide

A tunnel entrance in Big Walk

Quick Answer

Finish the Yellow route so the tunnel network opens, then walk into one of the network’s entrances. Big Tunnel is awarded by entering a tunnel zone, so placing the key, opening the gates or riding a Train through a railway tunnel is not the same thing.

Getting inside is the whole requirement.

Show Me the Entry StepBig Tunnel Not Unlocking?

This is one of the gameplay achievements. See the full achievements list

Where Are You Stuck?

Pick the line that matches your run. The tunnel network and the railway are different systems, and only one of them carries this achievement.

The Tunnels are still locked

That is a progression problem, not an achievement problem. Finish the Yellow Key route so the network opens.

Open Tunnels Guide

How to Unlock Big Tunnel

Three steps. Only the last one is the achievement trigger.

  1. 1. Unlock the Tunnel Network

    If the tunnels are still locked, finish the Yellow Key route first. That is what opens the underground network.

    Open Tunnels Guide

  2. 2. Go to an open entrance

    Use any open access point of the network rather than travelling back to one particular gate.

  3. 3. Walk inside

    Move through the entrance and into the tunnel. Getting inside is what registers the Tunnel medal.

If the achievement has not appeared, walk in through another open entrance before replaying the whole Yellow route.

Show Tunnel Access PointsYellow Area Walkthrough

What Actually Triggers Big Tunnel?

Big Tunnel is attached to the tunnel network itself, not to the Yellow Key.

The achievement comes from a trigger zone sitting in the tunnel itself. The Tunnel medal is awarded when your player enters that zone, which is why opening the network and earning the achievement are separate states.

Medal
Tunnel
Attached to
The tunnel entrances
Verified game-data detail

You do not need any of this to walk into a tunnel.

Component
MedalZone
Native event
MedalZone.OnEnter / OnEnable
Trigger surface
The tunnel network’s own entrances

Big Tunnel or a Train Tunnel?

Two different tunnels share one word, and only one of them is this achievement.

Big Tunnel

The underground network the Yellow route opens. Walking into it is what awards the medal.

Railway tunnel

Part of the Train route. Riding the Train through one belongs to the railway and does not award Big Tunnel.

Open Train Guide

Which Tunnel Entrances Count?

Use an entrance that belongs to the tunnel network the Yellow route opened.

The network has four coloured access points — Red, Green, Blue and Yellow — and they are all part of the same system. Nothing in the achievement condition names one of them, so you do not have to travel to a particular colour to get it.

A cave, a hole in the ground or any other underground corner is not the same as an entrance of this network.

Show Tunnel Access Points

Big Tunnel Not Unlocking?

Work down the list. The first line that is still true is the one to fix.

1. Is it actually part of the tunnel network?

A railway tunnel, a small cave or an ordinary underground room is not an entrance of this network, and none of them carries the Tunnel medal.

2. Is the network open?

If the entrances are still locked behind the Yellow route, this is a progression problem rather than an achievement problem.

Open Tunnels Guide

3. Did you walk inside?

Stopping at the mouth, standing under the arch or opening the gate leaves you outside the zone. Keep going until you are inside the tunnel.

4. Try another open entrance

The entrance zones belong to the network rather than to one gate, so walking in through a different access point is a reasonable way to retry the entry.

5. Platform achievement delayed?

The in-game medal and the Steam or PS5 notification can update at different times. Check your platform achievement list before replaying the whole Yellow route.

What Is Not Required

These come up often, but none of them is needed.

  • Walking the whole tunnel

    You do not have to come out the other side. Getting inside is what counts.

  • Every outlet in the network

    One entrance is enough. The achievement is not a tour of the network.

  • One specific colour

    Red, Green, Blue and Yellow access points belong to the same system, and no colour is required.

  • One specific entrance

    The Yellow route unlocks the network, but the achievement does not send you back to one particular gate.

  • A set time inside

    No number of seconds is required. Walk in far enough for the tunnel zone to register you.

Big Tunnel FAQ

Big Walk で「ビッグ・トンネル」を解放するには？

黄色いルートでトンネル網を開放し、入口のひとつに歩いて入ります。中に入った時点で Tunnel メダルが付与されます。

「トンネル網」を開放するだけで十分？

いいえ。ネットワークの開放と実績の獲得は別の状態です。メダルを発動させるのは入口区域であり、開放そのものではありません。

本当にトンネルの中に入る必要がある？

はい。入口や開いたゲートの前に立っているだけでは、まだ区域の外です。

列車のトンネルは対象になる？

いいえ。線路のトンネルは列車ルートのもので、「ビッグ・トンネル」は黄色いルートで開放される地下ネットワークから得られます。 列車ガイド

黄色いトンネル入口を使う必要はある？

いいえ。黄色いルートがネットワークを開放しますが、実績が特定のゲートを指定しているわけではありません。

トンネルの色は関係ある？

いいえ。4色のアクセスポイントは同じシステムの一部で、特定の色は必要ありません。

端まで歩ききる必要がある？

いいえ。反対側まで行くことは実績の条件に含まれていません。中に入ることが条件です。

すべてのトンネル出口を回る必要がある？

いいえ。入口はひとつで十分です。

ゲートを開けたのに「ビッグ・トンネル」が解放されないのはなぜ？

ネットワークの開放は前提条件であって、発動条件ではありません。どれかのトンネルの中に歩いて入る必要があります。 トンネルガイド

中に入ったのに「ビッグ・トンネル」が解放されないのはなぜ？

そのトンネルが鉄道ではなくこのネットワークのものか確認し、もう少し奥まで進むか、ほかの開いている入口を試してください。

Related

The Big Tunnel entry trigger and the network’s four access points last verified on 1 October 2026.

Where are you stuck?Tunnels guide