Blessed Spiders are encountered during and after the Underground Pass quest. They can still be fought after the quest is done. Unlike in RS2 they do not attack players, unless the player attacks them. They offer some
of the best combat xp in runescape classic. Though they offer no loot. A player is recomended to have a teleport to escape the underground pass when they are done fighting them.
It is recomended to follow this guide to get to blessed spiders.