Phimai Historical Park

This is the Khmer temple that came before Angkor Wat, and in places it clearly influenced it. The complex sits inside a rectangular walled compound, sandstone and laterite, with a central sanctuary tower and bas-reliefs working through Hindu and Buddhist stories. If you have any interest in Southeast Asian history, the carving alone justifies the trip out here. If you don't, an hour walking the pathways between the prangs, gateways and smaller shrines will still land, because the scale does the work for you.

Go early. Gates open at 07:30 and the compound has very little shade, so by mid-morning in the hot months you'll be moving from one bit of stone shadow to the next. Weekday mornings are the quietest. Signage gives you the historical context, and there's a small museum on site holding sculptures and artifacts recovered from the grounds, which is worth the extra twenty minutes. November to February is the comfortable window.