If you have a Slayer Ring or a fast way to fairy rings, you could use the back entrance a little north of the Slayer Cave entrance. Be warned that you will need climbing boots for this, and it is roughly double the time compared to Trollheim teleport. The first time you use this it may be confusing. Basically after you're on the path, you will see a little path shooting north. Enter the cave you see and you will be in the Torture Chamber of the Troll Stronghold. Run north and go up the stairs, then up the next set of stairs you see. Then run south and you should be familiar with where you are.