First of all you will need a Muster Card: Ruina Station, like this one:
You will also need to be level 75 and you will have only 30 mins to finish the dungeon.
Take Force Absorb Rings with you.
The entrance is where the blue ball on this map is:
Here is guide {how to finish dungeon}
here
BUT if you want to lvling fast you need 2-3 ppl in party and go as fast as possible to buffalos room and stay here till the end. With good party u can go to buffalos after 5-10 min and grind here 20-25 min.
Here i my video from buggalos room(as you can see i got about 5% in 20 seconds at lvl 95 )
http://www.xfire.com/video/1120e5/
