The 7 Adventures of Sinbad

In this modern day retelling of the Sinbad myth, Adrian Sinbad is a billionaire oil shipping magnate, the headstrong descendant of a long line of great mariners. When his flagship oil tanker is hijacked by Somalian pirates, Sinbad rushes to the rescue.But the tanker is pulled underwater by a giant squid, and sinks into a deep sea crater where a supernatural being of terrible power resides. Meanwhile Sinbad's helicopter is struck by lightning in a storm, and crashes into the sea.Sinbad comes to on a strange tropical island, and is immediately attacked by a monstrous crab three times his size. Narrowly escaping, Sinbad bands together with a ragged group of survivors: the helicopter pilot, his fetching science officer, the bitter tanker captain and the Somalian pirate leader (these last two, mortal enemies).But when he meets Loa, a beautiful jungle warrior, she shows him cave paintings which foretell the end of mankind. Sinbad must complete seven ordeals, or the world will be destroyed by Elmec Ishu, the supernatural being enraged by the sunken tanker. (Though the tanker hasn't yet spilled its full 130 million gallons of oil into the sea).A sudden earthquake strikes - and Sinbad and the group are plunged into the ocean, only to discover that the island is actually the back of a giant whale (as per the original mythology). But they're not in the water long before pterodactyls swoop down and carry them away to feed to their babies.They next encounter a cyclops, seductive sirens, and a bloodthirsty cult led by Loa's insane father (a la Apocalypse Now, in one of the best sequences of the movie). The group dies off one by one, while romance blossoms between Sinbad and Loa. Meanwhile, back on the mainland, the world is shaken by earthquakes and tsunamis; Emlec Ishu is increasingly angry about the tanker parked in its living room.Sinbad descends into a volcano in search of otherworldly crystals which hold the key to escaping the island. Nearly killed by a towering lava demon, he and Loa manage to flee with the crystals - which release superheated gas when water touches them - and finally get off the island, by means of an old hot air balloon.Returning to civilization, Sinbad's final ordeal is to somehow raise the tanker and thus avert the coming apocalypse. Setting out on a suicide mission, Sinbad and Loa pilot a small submarine four miles underwater to the tanker. But en route, the first of the tanker's bulkheads finally ruptures - spilling 450,000 gallons of oil - and causing Elmec Ishu to unleash his full wrath on humanity, in the form of armies of strange waterspouts which destroy everything in their path.Meanwhile, the sub is chased down and captured by the giant squid. But using the sub's external nozzle, Sinbad vacuums up several oil bubbles in the water outside, thus convincing the intelligent squid to release them. Sinbad and Loa reach the tanker, and start to drill into the seabed below it, where a seam of the otherworldly crystals is buried. As the waterspouts make landfall, and with the sub's power and air reserves nearing zero, the drill punches through and floods the crystals with sea water. Gas geysers erupt from the sea-floor, filling the tanker with air, causing it to rise to the surface. The world is saved, but Sinbad and Loa are dying, out of air four miles underwater. Until Elmec Ishu appears, and summons the giant squid back, to carry the sub to the surface.(by: IMDB user joemorph)

Question: Where does Sinbad look for otherworldy crystals?
Answer: Inside a volcano