Putting mods aside, there's not much you can do with it. If you have the Hearthfire DLC, you can invest it all into building a house and just buy whatever you need instead of gathering it yourself. I like to go around to weapon merchants and purchase weapons with enchantments that I don't already have yet, just for the sake of completion. If you enjoy stealth gameplay, dumping cash into alchemy ingredients for potions and poison could be entertaining. There's a perk in the pickpocket tree that allows you to reverse-pickpocket poisons onto NPCs which triggers the poison's effect. Other than that, I don't know. There's way too much gold in Skyrim and not enough to do with it. There are trade and economy mods that try to fix this which you can find a list of high-quality mods on the Skyrim Gems website.
I bought every house in the game, and I still had like 50k gold. The problem was that I had 99 smithing, which makes it way too easy to make money. I usually spent my gold on training after that, but I never got below 30k gold.
Well, I want your problem I could never seem to have enough. I kept selling and buying, selling and buying, and each house came slowly. Maybe because I was and am a hoarder. I simply store a lot of weapons and other stuff instead of selling them for gold.
Throw all your items/gold to a rushing river, wear the rags you were wearing during the introduction, and start a new life as a homeless wanderer. You'll need to restock your supplies, and you'll need to earn gold again because you need it to buy decent weapon and armors. Perfect combination, am I right? You get to remove your gold problem, and you get an exciting challenge ahead of you by being virtually back to level one.
I don't see how this is a problem. I also don't see a good way to avoid it. At some point you will accumulate more than you need as you level skills and complete objectives in game. Why does it even matter?