Third HP quest, need a party to do it. Go in Graah Castle, and on top floor, kill Graah for his hally. Sound simple and easy to do :)

Once you did get the hally, go on the first floor, in the middle you will see a well. Climb down, and go east.

Go trade the hally to Duke Moreal.

And again 100 more HP !

 
Note : You will loose those 100 HP each time you leave Cobrahn, but get them back each time you return to Cobrahn.