Drahtseilbahn Unterwasser–Iltios, Mountain funicular in Unterwasser, St. Gallen Canton, Switzerland.

The Drahtseilbahn Unterwasser-Iltios, known as the Iltiosbahn, is a funicular railway in Unterwasser in the Obertoggenburg region of the Swiss canton of St. Gallen. Its 1195-metre line runs from 911 m above sea level below the Früeweid to the Iltios mountain station at 1339 m. Two carriages carry 100 people each, giving a capacity of 850 people per hour per direction.

The funicular opened in 1934, built by AG Drahtseilbahn Unterwasser-Iltios. A 1991 merger with the Chäserruggbahn company created Bergbahnen Unterwasser-Iltios-Chäserrugg AG (BUIC). In summer 2005 the track gauge was widened from 800 to 1000 mm. Toggenburg Bergbahnen AG took over in 2008; after a pause from Easter 2024, service resumed on 14 December 2024 with new carriages and a valley station by Herzog & de Meuron.

The line is part of the Obertoggenburg ski area, which joins the pistes of Wildhaus, Unterwasser and Alt St. Johann. At the Iltios mountain station a cross-country ski trail starts toward Alp Selamatt. In the 2005/2006 season the funicular made 21,560 trips on 284 days and carried 351,849 passengers.

The valley station lies at 911 m below the Früeweid in Unterwasser; the mountain station Iltios is at 1339 m. From Iltios, the Chäserrugg aerial cableway continues to the 2262 m summit, and cross-country ski trails start toward Alp Selamatt. Service was suspended from Easter 2024 and resumed on 14 December 2024 after the valley station, designed by Herzog & de Meuron, was rebuilt.

The funicular's two carriages each weigh seven tonnes; one of these historic vehicles was transferred to the Seilbahnmuseum Kandersteg, while the second initially remained in the Toggenburg. The valley station was rebuilt to a design by the architects Herzog & de Meuron, and service resumed on 14 December 2024 after a pause from Easter 2024.