The Amazing Khmer
Of course, see the many major sites at Angkor which far surpasses the building of the Incas and every other culture of the period; now the roads and paths with both minor and major outposts and temples that connected the far outposts of the Khmer are just being found using satellite to ground radar.
Easy to see the almost east to west line of these connections from the spectacular Phra Viharn south of Si Saket to Phanom Rung near Buriram to Pimai near Korat to the far western outposts of the Khmer Empire and the ruins at Lop Buri. The distances of these connections show the tremendous extent of Khmer culture.
Major outposts of the Khmer with temples are hallmarked by their grand vistas. The Khmer, as the greatest culture and builders of their period, have been seriously neglected. The connections from distant "outposts" back to the center of power at Angkor are many when driving around Issan (north-eastern Thailand). Each is certainly worth the time to stop and wonder at the abilities of their builders.
Too bad our modern builders cannot seem to complete a four lane highway from Korat to Ubon Rathchatani; someday this will happen as major infrastructure projects are finally brought to and completed in Issan.
Thailand is truly a multicultural society that has come together from a variety of peoples, tribes, and cultures all bringing their talents to modern Thailand.