. Khammouane province covers an area of and is mostly of forested mountainous terrain. The province is bordered by
Bolikhamsai province to the north and northwest,
Vietnam to the east,
Savannakhet province to the south, and
Thailand to the west. Streams flow through the province to join the Mekong River. Some rivers originating in the mountains of the province are the
Xebangfay River ( long),
Nam Hinboun,
Nam Theun, and
Nam Ngum River. Between the Mekong and the
Annamite Range, the Khammouane Plateau features gorges, grottoes, jungles, limestone hills, and rivers.
Thakhek, the provincial capital, is on the Mekong River bordering Thailand. The border checkpoint is near
Nakhon Phanom. The city features buildings designed in the
French colonial architectural style. Tham Khonglor Cave (literally: 'beauty in the dark') is part of the National Protected Forest Area at Hinboun Mountain. Its west entrance is from Ban Khonglor village in
Hinboun District, while the east entrance is from Ban Natan village,
Nakai District. The cave runs for a length of about . The Hinboun River flows through the cave perennially. Vang That and Had Xay Luang are the two hanging rock formations in the cave. The cave is approachable along two routes, one from
Vientiane along
Route 13 to Hinboun District, and the second route is by boat along the Hinboun River. Khammouane Thakhek2 tango7174.jpg|
Thakhek Khammouane NamHinboun1 tango7174.jpg|Hinboun River Khammouane ThamKhongLor2 tango7174.jpg|Tham Khonglor Khammouane BanNatan1 tango7174.jpg|Ban Natan ==Protected areas==