When I was a kid we built a fort completely out of HVAC units.
We lived out in the middle of nowhere, and oftentimes me and my friends had to get creative with our games.
One day while exploring the forest we found a large shipping container full of HVAC units. There were several central air conditioners and window air conditioners on one side of the crane. We pulled out all the central air conditioners and used them as a foundation for the fortt. Then we built onto the central air conditioners with the window air conditioners. After we emptied all the air conditioners out of the crate, we looked at the furnaces. There were hot water boilers, gas furnaces, oil furnaces, and electric furnaces. We used The gas furnaces and oil furnaces for a blockade. Then we took out the hot water boilers and made a large wall all the way around our forte between the trees. Our last mission was to figure out how to incorporate the air purification systems into our fort. We took out some of the air filters and used them as small windows between window air conditioners and central air conditioners. We also use some of the heating and cooling equipment to build pretend rooms and weaponry quarters. By the end of the day we had a huge fort made completely out of air conditioners, air purification systems, and furnaces. We had some friends who also used some of the HVAC units to build their own fort and we had several battles. It turns out that air conditioners and furnaces work great as forts.