This portion of the Luigi's Mansion 3 guide covers the Boilerworks Walkthrough and all the Boilerworks gems (note: not all of these can be collected on the first run so you'll have to come back ...

Squish Gooigi through the bars and have him pull the ball and cord so Luigi can get through. Once you get to 6th floor, Castle MacFrights, head to the right. Use Gooigi to move through the bars. Then ...