I am the level 314 guy here. So you want to level up some skills to make legendary?
Then finding hard dungeon is NOT the way.
Rising one hand and two hand and archery is very difficult and take a long time.
Instead, do one of these two.
With restoration glitch.
There are plenty on videos and details on how to do so https://www.google.com/search?channel=crow2&client=firefox-b-d&q=restoration+glitch+skyrim
Technically, it's lore friendly.
With restoration glitch, create fortify enchanting potion. Something like 10k % is enough. Now, after that, enchance one ring with enchance alchemy.
Now use that ring anytime to create potion. Here is the trick.
Speech, alchemy, smithing and enchanting have this rule. Your skill increase proportional to the value of items created.
That means, with 10k% fortify alchemy, for example, you can create one potion and if that potion worth 500k septim (I'll write that $500k, assuming one septim is about one dollar), you will increase your alchemy from 15 to 100 with one or two potions.
After that? Sell the potion. Again, each time you do so, you increase speech from 15 to 100.
Of course, you can also do that with enchanting and smithing. However, that's a bit more difficult. It's much easier doing it with alchemy.
Fortify restoration is a must. You get an OP character that can one shot everything. Unfortunately, even though you have 10k% improved archery gauntlet, you don't increase archery from 15-100 at one shot. So archery is not like speech and alchemy.
Without restoration glitch
Bbbbbbbbbbuuuuttttttt you're a pious lore friendly guy that wants to do this without glitch.
Max out your illusion skill. Illusion is the only school of magic I know that works. Maybe other works too I don't know. Get the master spell harmony.
Now go to a place with lots of people. I usually went to basement of solitude. However, if you know any other places, that's good too. Make sure it's a lot of people there peacefully.
A good complement of this answer will be such places. Basically, I have completed storm cloak campaign and all the defeated jarl is in the basement of solitude so it works for ME. Not necessarily for you.
Now cast harmony 7 times. Yap. Just 7 times. And you will increase illusion from 15 to 100. At less crowded places you will have to do this, 8 times. You can wait 1 hour if you run out of magicka. I simply used a helm with 10k%+ magicka so not an issue for me.
Took like 30 seconds per try.
That way you get a huge level fast.
You see the pic I showed? It shows how I make alchemy and speech legendary so many times. Then I also make illusion legendary like 4 times.
By that time my level is already so high and I got all the perk. I actually have to weaken my character and fight naked for the game to feel normal again. Otherwise, I just one shot everything.
So diplomatic immunity quest is just so easy for me. He he he he.
Other ways to increase skills
Other answers say you got to pick a tanky or tough opponent. I totally disagree. The best way to raise skills is NOT to kill tough opponents but weak opponents. Your skill increase in one hand, two hands, destruction, and archery does not depends on how tough your opponents are. It depends on how much the base damage of your weapons are.
In other words, unlike in most games where you have to fight top opponents to increase skills, in Skyrim, you can just find weak enemies and practice there. That is. Mudcrab, spiders, animals. Mammoth are fine. You want to beat up the enemy several time.
So bound sword, bound axe, and bound bows, all have near the top base damage in the game. You do not increase skills faster by enchanting or smithing your weapon. Hence, I suggest using unimproved weapons or bound weapons.
I think bound bows have like the best DPS in the game. Bound sword is close to the best sword out there. Bound axe is also near the top. The top two hand is Dragon Bone Warhammer according to this.
Because I like to raise all skills to 100, I use Dragon Bone Warhammer to increase my two hand. After that, I do NOT want to make that legendary.