Money making guide/Cremating urium remains
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Cremating urium remains, collecting the keys and opening the Gold Chests in the Shade Catacombs, rewards a large number of coins and alchable items as well as a decent amount of Firemaking and Prayer experience. Chests can also reward pieces of the Zealot's robes, which is the Prayer skilling outfit.
Players interested in clues can expect roughly one elite clue every 35 minutes. If you are very quick at completing clues this can be more profitable. For a guide that factors in the time to complete those clues see Money_making_guide/Completing elite clues (urium remains)
For free transportation, Morytania legs 3 or better is the best way to get to Mort'ton regularly. Mort'ton teleports are also an option, but at 49,024 each they are fairly expensive and will reduce the hourly profit by a lot, for only 20 or so seconds saved per trip.
To cremate the shades, fill up the gold coffin with 28 urium remains and fill the rest of the inventory with redwood pyre logs and a tinderbox. Use the logs and remains on the pyre and light it, collecting the reward (either coins or a gold key) from the pedestal. You can stack up multiple rewards on the pedestal to save time, but the loot will disappear after 5 minutes. Tick manipulation methods can be used to slightly increase the speed the shades are cremated, up to around 400 cremations + loots per hour, or 600 cremations without chests.
You can either bank the keys or go open chests directly from there. They are about the same overall speed, although saving up keys can lead to more efficient chest opening because you won't have to switch chest types as often and instead of running a partial inventory of keys while getting coin drops, more keys can be used in one run. Either way, enter the Shade Catacombs, go through the gold door, and start opening chests. Each loot will give coins, swamp paste, and one other item – none of them are incredibly valuable (besides the elite clue), but they all add up to make each chest well over 10,000 on average.