Stingray (1964)

S1E4 Subterranean Sea

After their holiday plans fall through, the crew of Stingray ventures into the ocean's depths. They stumble upon a deep shaft that opens into arid plateaus. Just as they begin their exploration, a massive wall of water transforms the desert into a hidden underwater sea. Racing against time, they swim back to Stingray, striving to find the shaft before their oxygen dwindles. In a moment of urgency, they dive into the first shaft they encounter, surfacing near a stunning tropical island—an idyllic spot for a vacation after all.