Subwayne Old Gotham North unlocks by breaking open the pipe above the civilians, turning the wheel on top of the building to flood the partying civilians, then using Commissioner Gordon’s glue gun to stop the water flow so you can press the button and open the shutter. This opens the Old Gotham North fast-travel tunnel in LEGO Batman: Legacy of the Dark Knight.
How to unlock Subwayne Old Gotham North
Step 1: Reach the Old Gotham North SubWayne

Head to the Old Gotham North fast-travel station in Gotham and interact with the shutter area where the “Unlock the shutter to the tunnel” objective appears.

The station is one of the game’s SubWayne fast-travel points, and Old Gotham North is among the Gotham locations with unlocked tunnels.
Step 2: Break open the pipe above the civilians
Firstly, use Batman to break open the pipe above the partying civilians. The water wouldn’t start flowing yet. For this you’ll have to access the wheel on top of the the building.

Step 3: Climb on top of the building
Next, get to the top of the building.

As always, use grapple or any other means. Just get up.
Step 4: Turn the wheel
Find the wheel and turn it to start dumping water over the civilians partying nearby.

This is the trigger that changes the puzzle state and exposes the next interaction, so make sure the water is visibly flowing before moving on.

Step 5: Switch to Commissioner Gordon
Swap to Commissioner Gordon once the water is running, because his glue gun is required to stop the flow. If Gordon is not in your current team setup, progress the story until his toolkit is available, since some SubWayne puzzles depend on character-specific gadgets.

Step 6 Stop the water flow with the glue gun
Aim Gordon’s glue gun at the water mechanism to seal it off. The puzzle will not advance if the water keeps running, so this step is the actual gate between the wheel action and the shutter button.

After the water is stopped, press the button by the shutter to open the tunnel.

Once the shutter lifts, the Old Gotham North SubWayne is unlocked and becomes available as a fast-travel point.

Critical mistakes to avoid
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Do not try to press the shutter button before stopping the water; the puzzle will stay locked.
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If the wheel seems inactive, make sure you are at the correct SubWayne station in Old Gotham North and not another Gotham fast-travel point.
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If Gordon’s gadget does not work, you may need to re-select him or progress far enough for the required tool to be available.
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Some SubWayne stations in the game require story progression or specific characters, so not every tunnel can be unlocked immediately.
Unlocking Old Gotham North saves travel time in Gotham and brings you one step closer to full SubWayne completion, which is required for the fast-travel trophy and easier open-world cleanup.