Despite this movie being a sequel to Journey to the Center of the Earth (2008), Josh Hutcherson is the only actor to return from that movie.
(at around 46 mins) The scene when they are walking to find the submarine, you can see the wide open space where they filmed Jurassic Park (1993). That open space is where the dinosaurs are on a stampede.
The original Jules Verne story, Journey to the Center of the Earth (1864), on which Journey to the Center of the Earth (2008) was loosely based, never had a sequel. However, another Jules Verne story, 20,000 Leagues Under the Sea (1870), did have a sequel, called "The Mysterious Island", which was released in 1874. The book followed five American men stranded on an island in the South Pacific, which is similar to a plot point in this movie.
There is another Jules Verne novel titled "The Golden Volcano", which, although is set in the Canadian Arctic during the gold rush, spews gold nuggets when it erupts. This is likely where the mountains of gold came from for this movie.
Hank Dwayne Johnson says the he's the 3 time recipient of the esteemed Rochefort Award. This is a real thing. It's named for Capt Joseph Rochefort, USN, who was a pioneer of Naval code breakers called Cryptologists (now called Information Warfare Officers). Captain Rochefort and his team broke the Japanese code indicating they planned to attack Midway Island in WW2.