Retro + faux, something which references a fake/non-existent past. Used to describe an object or especially a place/area which is made to evoke a version of the past which only ever existed in popular imagination and not in reality.
"Meh, that Wild West theme park was totally retreaux"
"How so?"
"I'm pretty sure not everyone in those days had to choose between being a cowboy, outlaw, grizzled old prospector, or working in a saloon."
A Shackteau is a humble, weather-beaten, structurally questionable shelter located in a spectacular or highly coveted place—Wales, Jackson Hole, Sun Valley, Crested Butte, coastal Maine, the Alps—where the building itself may be worth almost nothing, but the dirt, view, access, and mythology make it absurdly valuable.
In use:
Shackteâu - We thought it was an abandoned shed until the realtor called it a rare alpine Shackteâu with unobstructed views and listed it for $2 million.