You reach it from the second island (I think it's the second) which you reach after jumping into the water. Up the hill you'll see a ruined building (which is what the clue is referring to), ignore the two portals you see there and go straight ahead. You'll meet several groups of mobs along a causeway-like path and then you'll meet a path heading off to the right. Bear left and you should see not too far ahead the shard's light effect. There are more groups of mobs to avoid.

I have run through the mobs and lived, you can get to a point where you can shake them off but more than likely if you're on your own, on-level or thereabouts, you'll need at least one 'raise' (using a soulshard or the Soul Trap skill line perk).

You can Stealth your way past nearly all the trash if you have that skill maxed (on a cat for example).