The pier repeatedly seen in the background by the beach is the Paradise Cove Pier in Malibu, CA. It was torn in half by a giant El Nino wave in the '80s.
When Ethel and Mr. Grant meet in the roadhouse, the exterior sign says "Jefty's Roadhouse"-- a stock shot from Road House (1948) with Richard Widmark as "Jefty".
The monster in a rubber suit was performed by a female, Norma Hanson. The only known instance of that casting decision being found.
Together with The Fast and the Furious (1954), this was one of the first films to be distributed by the American Releasing Company which would later become American-International Pictures.
10,000 leagues = 182283465 feet, well below the depth accessible with scuba gear. Need to add that depth is equal to 34,500 miles. The center of the earth is only about 4,000 miles.