Located southeast of Windhelm, the mine borders a small mountain range and a small Orc village called Narzulbur. It is extremely rich in Ebony ore. If you haven’t made friends with Orcs yet, they will berate you and tell you that you shouldn’t be there. Ignore them – you can collect enough Ebony Ore to build an entire set of armor, one weapon, and about four upgrades. You can find 48 to 60 ebony ore here (with the higher number perhaps depending on if you’re willing to steal). There is even one particular minehead which has 4 ebony veins clustered together (at the center of the top-down map, but high up within the mine; watch out for the hole in the floor). Unlike many veins in Skyrim, Gloomwater has small veins clustered together, so look carefully. It also has a number of iron veins.
You may have trouble with orcs mining during the day, making it so that you cannot mine those nodes. You can stand between the vein and orc and repeatedly bump against the orc, or you can deactivate the torch near the entrance, making it dark and they will leave, or just move on to another vein and come back to their vein later.
There is a forge outside the mine, and a shack near the entrance has a copy of Heavy Armor Forging, a skill book for smithing. There are also several Ebony ores in the cart by the mine entrance and the table by the forge.