I'm at the same stage in this, my second playthrough. I've found the altar, but there's a bunch of Draugr spawns around the altar, not to mention abomination spawns. I've placed the portal at a secure place, and have been busy destroying all the spawn locations around the altar. ...just to make things easier. ..otoh I'm still mostly in troll armour, so there are different ways to prepare oneself. I just know that stamina is costly in the swamp, and I don't want to pick more fights that necessary...

edit: yea a mace or hammer is probably wise to bring too