Are there caves underwater

Answer 1

Yeah. They show them in movies and National Geographic sometimes.

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You divide them into two categories, rather simply.

Many caves on land have "sumps" - permanently water-filled stretches of passage, usually rather like an elongated and enlarged version of the U-bend under a kitchen sink. Some cave streams emerge from sumps at their risings (springs). In a few cases, where the cave is situated at low altitude, the sump may even dip below sea-level though with no direct link to the sea. The deepest sumps in Wookey Hole, in S.W. England do that, I believe. They do so because the rock strata dip steeply, forcing passage development to follow a zig-zag course on a vertical plane.

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The other category is the cave originally formed on land at a time of low-sea-level and now below sea-level. The sign that this happened is the presence of submerged stalactites and stalagmites, which do not form underwater. Some of the largest of these are found in The Bahamas and Florida.