Instead of "leaving and returning" to the sublocation, you CAN, instead, just refresh the loading page that tells you that you are exploring the Hidden tunnels of bamboozle at level 10 (? levels above/below your own level)
Hit refresh until it chooses a level you're comfortable with. Please note, there are alot of BOSS fights in sublocations, there are also HEROES. HEROES are monsters that have higher attack/defense than normal monsters their level, and are harder to kill.
Generally speaking, I choose to explore sublocations at -2 currently, until I get better gear/armor/spells.