The Sip 'n Dip Lounge is a tiki bar in Great Falls, Montana, US, opened in 1962, when Polynesian themes were popular. It has survived to the present day with its tiki theme intact. Located inside a local motel that was considered modern and trendy at the time it was built, the Sip 'n Dip is known for having people dressed as mermaids swimming underwater in an indoor swimming pool visible through a window in the bar. Decorated with a bamboo ceiling and a South Seas theme, the bar featured "Piano Pat" Spoonheim, noted for her unique "jazzy" style, who played piano there from 1963 until her death in May 2021.

The mermaid concept was introduced in 1995 when there was a revival of the tiki fad and was the brainchild of the bar's current owner who wanted to add a "fun factor". It became popular, particularly for Montana, a landlocked northern state where a tropical tiki theme is unexpected. Beginning in 2003, the bar began to gain prominence outside Montana, when the magazine GQ listed the lounge in its list of the top ten bars in the world, ranking it as the "#1 bar...worth flying for". The bar usually employs six women, who wear mermaid outfits designed and hand-made by the bar's manager, Sandra Johnson-Thares. Mermen were brought back in 2016, having previously appeared on occasion from the late 1990s to 2004.

Celebrity patrons of the Sip 'n Dip have included the actors Nick Nolte and Daryl Hannah, who reprised her portrayal of a mermaid in Splash by swimming in the pool while wearing a mermaid tail. Both actors signed the glass window, though their autographs were lost two years later when the window cracked, forcing the pool to be drained and repaired and the double-paned glass replaced with a triple-paned version.

The establishment features a glass wall behind the bar looking into an indoor swimming pool where swimmers can be seen under water.[1] It is located inside the O'Haire Motor Inn, which was built in 1962. The concept of a swimming pool designed so that underwater swimmers can be viewed from inside the bar was original to the building, as the person who built the O'Haire had been inspired by a similar design he saw when visiting the Playboy Club in Chicago.[2] When built in the 1960s, the O'Haire Motor Inn was considered "swank" and modern,[3] and the tiki concept was popular, in part due to the then-recent admission of Hawaii to the United States as a state. The tropical theme was also viewed as a fun concept for Montana,[4] a landlocked state with long, cold winters.[5]

Though tiki bars in general declined in popularity in the late 1970s and 1980s until the revival of the style in the 1990s,[6] the Sip 'n Dip survived with few changes.[3] During the 1990s, the idea of having mermaids swim in the pool during evening bar hours was the brainchild of the bar's general manager, Sandra Johnson-Thares, and her mother, who wanted to add a "fun factor". It began with a single "mermaid" in the pool on New Year's Eve in 1995. Today, Johnson-Thares makes the mermaid costumes herself and said, "I never in my life believed the mermaid attraction would be such a big hit. People are fascinated with them, and it's not something you'd expect to see in Montana."[1]

The bar has a bamboo ceiling,[3] traditional cocktails, local Montana microbrews and specialty drinks such as the "fish bowl",[7] a 64 US fl oz (1.9 L) cocktail[8] that has nine shots of different liquors.[7] It also has an outdoor patio open during the summer, from June to September.