Continuity mistake: In the scene where Sean wakes up on the beach, he is lying face down in the sand beside a fish, and he is wearing gloves. In the next shot they are gone and reappear again in the following shot. (01:00:20)
Continuity mistake: When Trevor is fighting off the carnivorous plants that are attacking him and holding Hannah hostage, in one shot we see him punch into the mouth of one plant, causing his hand to become entirely covered in a sticky goo. In the following shots however, the same hand is now clean. (01:01:55)
Continuity mistake: When Sean is jumping across the floating magnetic rocks, as he jumps on the one that begins to flip him around twice, as he is flipped round the first time, it causes his small black utility belt (with the pocketknife and phone pouch) to fall off his waist, down into the abyss. In the following scenes moments later though, the same pouch/belt can be seen on his waist. (01:05:15)
Revealing mistake: After Trevor has been lowered above the pit of magma, in an attempt to light the magnesium walls with a flare, we see shots of Sean hanging over the edge of the inside of the T-Rex skull. Sean's hands are resting on a large tooth in the skull, which clearly shakes like a fake prop each time he touches it. (01:17:15)
Continuity mistake: When Trevor, Hannah and Sean are being pushed up in the T-Rex skull by the geyser, they are laying in the skull and you can see that there is harness rope that comes out from behind Trevor and Hannah's back (that they are laying on). But in the shot when they are pushed out the mountain by the geyser and reach their highest point (before they start falling back down to the ground again) there is no rope visible behind them or in the skull at all. In the following shot as they fall back down to the ground, the rope has reappeared. (01:17:35 - 01:18:20)
Continuity mistake: After Trevor, Hannah and Sean are forced out of the mountain (inside the T-Rex skull) by the pressure of the geyser, as they fall back down to the ground, they begin to slide through shrubbery. Between shots as they slide through, the amount of greenery and leaves that is inside the skull keeps changing from hardly any, to a lot, etc. (01:18:20)
Continuity mistake: As the T-Rex skull comes to a sliding stop at the bottom of the hill, Trevor, Sean and Hannah get splattered by berries. In the first shot there are a lot of berries on Trevor's shirt and face, then in the next shot there is hardly any and then there's a lot again in the third shot. (01:18:35)
Factual error: Trevor - a Professor of Geology - boasts about having an article published in Scientific American, and that is not something any scientist would do. Scientific American is looked upon with slight disdain by the scientific community, considered to be a populist crowd pleaser. It is not even peer reviewed. Considering that he has just turned the geological and archaeological worlds on their heads he would have been better off publishing in Journal of Geological Research or Geology, both prestigious professional journals.
Factual error: Hannah's full name is Hannah Ásgeirsson. Icelandic surnames are (Father's name) sson for boys and (Mother's name) dottir for girls, so Ásgeirsson would be the surname of the male child of a man named Ásgeir. Her name should be Hannah Sigurbjörnsdóttir.
Factual error: While magnesium is the seventh most abundant element in the Earth's crust, it never occurs naturally in the uncombined state because it is too reactive. Therefore, there are never veins of magnesium metal to be ignited. Magnesium metal (uncombined state) will burn if ignited.
Continuity mistake: When Sean is jumping around the floating, magnetic rocks, a piece breaks off and falls. Why does it fall? It would just float next to the big one - held up by the magnetism. It might even float higher up, since Sean's weight should affect the bigger piece a bit.
Other mistake: When sitting on the beach looking at Max's notes, they mention that it is 95F. But nevertheless none of them appear to be sweating. Their skin is dry, and Trevor is wearing a big sweater.
Plot hole: We don't see any herbivores in the underground world - just fish and little birds. A T-Rex would need lots of big game to survive.
Factual error: It is impossible to receive a cell phone call at the center of the earth. There is no way that a signal can penetrate thousands of kilometers underground like that.
Factual error: Diamonds, emeralds, and rubies do not occur together, they form under very different conditions.
Factual error: The mountain guide seems to prefer SureFire flashlights, carrying an M6 Guardian. Later on, they find Max's camp in the centre of the Earth and the guide picks up another dirt-covered M6 that belonged to Max. Max went missing in 1997, 3-4 years before SureFire produced that light, so he couldn't have had one.
Continuity mistake: In the scene in Trevor's apartment, when he is leafing through the Jules Verne book, between shots he is looking in very different sections of the book. In one clip some of the first pages, next clip in the middle, then back to first pages.
Continuity mistake: When Sean first sees the 'magnetic rocks' forming a bridge across the chasm, there is a great distance between him and the other side, and about 20 floating rocks. When he starts to cross, the distance is now much shorter, and he only jumps on 6 or 7 rocks to get across.
Plot hole: When falling into the deep, deep hole, the three would be killed upon impact, and the fact that they follow water will not change anything. They will still be falling with more than 180 km/h. The water isn't slowing them down, as nothing is holding the water up. So it will be free-falling too - with more or less the same speed.
Plot hole: While the slopes on the mine tracks make for a thrilling downhill ride, the cars loaded with ore could never have made it back up the tracks.
Answer: A mountain.