Hello all.
Before we begin, you should all know the Req's for defeating Tarn, and also why this is useful
Requirements:
Haunted Mine Quest Complete
40 Slayer
High enough combat stats to defeat Tarn (Level 69) And run past Terror Dogs (100+)
You should be aware before attempting this, that Tarns Lair is a dangerous place and if you die you will loose your items.
Why should I defeat Tarn?
Killing Tarn is very useful. You can only defeat him once, yielding a 5K Slayer EXP Reward and once you have done so, you may pick up Tarns Diary from the table behind him.
Tarn's Diary allows you to enchant your Salve Ammy, so that you have Salve Amulet (e). This change allows you to do 20% Extra damage to undead, as opposed to the 15% previously.
How to get there.
There are in fact 2 ways to get there. The first way would take too long to explain, and it is a lot of walking through zealots mine. Alternatively, you can use the method I would prefer.
Buy a Ring of Slaying (Or make one, providing you have the ability to do so) And use it to teleport directly outside of Tarns Lair.
Now, Tarn is a very easy monster. He has 2 forms, both needing 40 slayer to attack. He isn't hard, a whip and rune at the very least could manage it. Just watch your health against those terror dogs, and take a few prayer potions. You could also choose to take 100 GP, for access to the bank down there.
Take a teleport if you are unsure, but IMO Even a level 75 could manage this without a problem.
If you destroy the diary, you do not have to defeat Tarn again. You don't even need to mooch down there, you can get it back from the bookshelf in your player owned house.
Very simple guide but I hope it has helped,
Andy.