The specific Frostvenom spiders nest we’re after is found in the eastern part of this delve. From the entrance, just follow the path to your left side, hugging the wall. As you come across the second pool of water, immediately turn left, and you’ll spot a small cave entrance covered in the spiderwebs. Without the map, this pathway would be rather well-hidden. Go through it, deal with the two spiders that might follow you from the back, and reach the end of the path. Its end is overlooking the water down below, and is also the location of the skyshard we are here for.
If you are a fan of achievements, there is also an instrument in the easternmost part of the delve, the one you’ve just passed several steps ago. It’s a part of the Instrumental Triumph achievement, where you have to collect 19 instruments.