HO, Southern Pacific / New Zealand combined (a what if scenario: after WWII New Zealand was so damaged that the USA rebuilt the railroads and owned them).

SPL opening ceremony - note the chicken on top of the depot

Single loop, one town, a small yard, three staging tracks at back of the loop (crawl-under access).
A bigger space in the basement, but cold, dusty, damp, remote from the family (the basement has only exterior access), so eventually abandoned.

Was constructed with steel wall-framing and styrofoam. MDF backdrop, joints cracked in the heat. MDF valence and fascia worked great for long sweeping curves (I got the MDF pre-cut by a kitchen joinery shop). Black curtains looked superb but showed dust a bit.

Lesson learnt: know when to pull the plug.

Status

Dismantled. I now have a well-lit workshop.