I was thinking about making a landmark for the last Tripodician building, a stone ziggurat made of unusually study blocks. It's really detailed, too, with notes on the local flora of the ziggurat, its decay, the chambers underneath it, and the last Tripodician of a moon-worshipping tribe, an albino nicknamed "White Bone" who left extensive diagrammatic warnings of the solar flare's dangers to any future visitors.
However, given Tripodicians went extinct in Generation 145 and it's Generation 164 now, even an unusually sturdy, lucky, huge ziggurat would be long since broken down. I doubt it would even leave traces of unusual geology at this point.
Since it's long, long past the point at which any Tripodician buildings would remain, I can't make a landmark for them. Should there be a "Sophont Archaeology" topic?