East of Thakhek, potholed Route 12 is swallowed up by a surreal landscape of karst formations. Hidden among the sea of jagged limestone hills are the Mahaxai Caves, many of which lie within the Khammouane Limestone NBCA. A number of the more easily accessible caves are popular both with Lao families on a weekend picnic and with foreign tourists. These more visited caves line the Thakhek–Mahaxai road, the furthest one only about 20km from Thakhek. The best caves here are spectacular and a day-trip out to explore them is a must if you’re staying in Thakhek.

The easiest way to reach the caves is by renting a motorbike or chartering a tuk-tuk from Thakhek, but some visitors prefer to cycle out or catch a Mahaxai-bound bus to the caves and then explore on foot. Public transport can be tricky, however: pick-ups and buses travel the road frequently enough in the morning but aren’t so reliable late in the afternoon. To get back, you’ll have to flag down one of the buses or pick-ups coming from Mahaxai – of which there are several a day – although again, you can’t count on catching one late in the afternoon. If you want to do a walking tour of the caves, a good starting point is Tham Ban Tham, on the road to Mahaxai 7km from Thakhek; from here you can walk to Tham En, taking in other caves en route, a 12km walk in all.