A grim cave site north of Phonsavan, on the road to Muang Kham. On 24 November 1968 an American T-28 fired a rocket directly into the mouth of Tham Piu, killing more than 350 villagers who had taken shelter inside. The cave was sealed off by the blast and was only excavated in the 1990s.
A small monument and a single Lao language plaque mark the spot. The cave itself can be entered with care — there is little to see beyond the entry chamber — but the site is included on most full-day tours out of Phonsavan and is worth the stop for the perspective it gives on the rest of the regional history.