HO train enthusiasts?
In a little more than 2x8 for HO, I'd suggest a "timesaver".
It's a switching puzzle, so you don't get bored watching the train chase it's tail.
John Allen's Gorre and Daphetid Railroad - The TimeSaver
That's what I did to get my chops up getting back into it in the early 2000's.
I put scenery on mine and added things like a tank car unloading platform, small freight house, team track ramp, etc.
...and mine had an interchange track at the top center.
I also used more realistic looking manual ground throws for the switches/turnouts.