Fairlie Fourplex
Currently fiction-based, a Fairlie Fourplex is an engine with four sets of bumpers, four sets of boilers, and etc. It's built like two Fairlie Duplex engines overlapping and welded to each other at a 90-degree angle. It can only be placed on a railroad diamond but isn't mobile due to its design.
If you want to build a train, only to not use it to go places, you might as well make a Fairlie Fourplex.