A sophisticated civilization spawns Stonehenge over many centuries… but disappears from any radar.
The Stonehenge edifice itself seems to have been a spiritual/religious/astronomical edifice, marking, as well, seasonal solstices via the sun’s projection through its carefully laid out architectural apertures.
Edifices with a similar sun–centered spiritual/religious/astronomical dimension will manifest later in world history around the globe, including the well–known Incan Machu Picchu complex in the Andes Mountains, halfway around the world, 4,000 years later.