What lvl do you need to be to do that dungeon I never made it even against the battle horrors my party is average lvl 4, 5

It's part of expansion so it's supposed to be able during end-game. You need quite a higher level and even then it's hard unless you know what to do.
Although it's in the middle of map you are supposed to go there after visiting Ulgoth's Beard.

thanks for the quick reply i had a feeling that it was going to be hard but i have to say sometimes i still find monsters strong i came to an area once and there were basilisks i hate those instant death attacks. But it makes it a very big challance.

you can defend yourselves against the stone gaze (or whatever the name was) with the 1st level spell "protection from petrification", this grants immunity against basilisks so you can do whatever you want with them afterwards.

i think my party members were on level 7 when entering the durlag's tower (4 member party).

uhm have to look up where i can get that it sounds like a cleric spell or is it a mage?

mage, don't remember exactly where you can get one but i'd try High Hedge, Sorcerous Sundries in BG if you have access there or some temple.

i have most of the areas except cloud something forgot the name where you can get coran i dont know how to unlock that area

In addition to the mage spell that protects from petrification, a potion of mirrored eyes does the trick. Also, you can get those scrolls that are usable by everyone (the dark yellow ones with the green symbols) with protection from petrification.

thanks m8 for the help cause i think those basilisk are good for xp :)

Also in the most basilisk heavy area (East of temple near Beregost) there is ghoul you can persuade to help you and he is immune to bazilisks' attacks and you can use him to mop the area up.

nope your wrong it is a lvl 1 spell so i could cast it 4 times wich i used on my meleers killed them all and finished the bandit camp and now that invoker can cast fireball and lighning bolt finaly :) Now i only need to get more gold because there is a shadow armour with my name on it :)

wow i replaced that paladin with coran, coran and kavin or how the other archer is called are a lethal team mostly i cant even get to the enemy and that 2 fellows has killed them already.

yeah bows are very effective in BG1 and since coran and kivan both have high dexterity they get bonus to ranged THAC0 as well (coran +3 and kivan +2).

edit:
actually coran gets +4 and kivan +3, i forgot they were elves which gives +1 to bows/long sword as a racial bonus.

On the basilisk infested map, you don't need to protect the whole party. Basilisks are one-trick ponies. I don't think they have any attacks that cause hp damage. Your best fighter can slaughter them solo if protected from petrification. Just keep the rest of your party a safe distance away.

You will still need more than one potion/spell/scroll to clear the map, because the duration will run out before you are done, but still there's no need to waste your resources protecting the entire party.

And there are still a few non-basilisk dangers that might kill your lone fighter, so a little scouting is in order with stealth or invisibility. And you can keep your the rest of your party close behind- they can follow just a few steps behind your protected fighter or scout, as long as they stop immediately when a basilisk is spotted (auto-pause on sighting enemy does the trick here).

As you noted, if you want to add some levels to your party quickly, the basilisk area gives you a lot of easy kills for really high experience, as long as you go prepared.