Charge Fire Orb is an enchantment spell that requires a Magic level of 63 to use. It can only be cast on a fire obelisk, deep in the Taverley Dungeon after passing the ladder to the water obelisk and the two black dragons in the dungeon on the main floor.
If a player has an Agility level of 80 (can be boosted at a minimum of 75 Agility), they can use the shortcut to there at the start of the entrance, as it's the fastest way of reaching the fire obelisk. The second best way if to have an Agility level of 70 (65 or higher if boosted) and use the pipe on the right. This will only be half a minute longer than using the higher level shortcut. If you don't meet any of these requirements, then fire orb running will be very long, as the dungeon is relatively long and can take around 3-5 minutes per inventory.