For this achievement you must beat each map on each difficulty level. The challenges are not part of it but there are achievements connected to certain maps using certain challenges. Doing a challenge can net you a good reward but will always make a map more difficult. For this achievement, it is highly advisable to avoid challenges at least until it is done.
A few tips:
Level up and return if it is too hard.
Level up your weapon and return if it is too hard.
Quit the level before failing or you lose experience earned which will only lengthen the game.
Pause the game and move your heroes. There is no reason to let it play while you do it.
Farm Angry Mobs on Town Gate. This is a great place to farm gold/gems as well. On easy, middle challenge, you get 5 gems (always the same per run) and 113 gold (may differ per run). This easily adds up to 300 gems 6600 gold an hr. Great way to get some more runes
When level 25ish, depending on runes, farm Chair Lift the middle challenge. Don't move yourself and work your way up to hard. Great farming area.
Around 40-45 you can start farming hard mode Castle. Load your last 3 characters final runes with pick pockets. Make sure Jack is loaded with damage/range runes and put him on the shrine that is available. You will likely hit 10 for charges and unlock another achievement as well.
Buying cheap rune packs and merging them is a great way to get runes. Unless you can buy the orange pack, buy those instead. They seem more worth the moneys.