Scryer's Tier is a terrace in Shattrath City, and the base of operations for the Scryers. At the center of the Tier is the Seer's Library, which serves as the faction's headquarters. Scryer's Tier also boasts an inn run by Innkeeper Haeltholand a variety of vendors, including reputation vendors and a reagent vendor behind the Seer's Library.
Scryer-favored players who wish to take the shortcut to Nagrand through the Aldor rise should be warned not to take the elevator between the Scryer's Tier and Aldor Rise, since aggroing the guards and getting Banished from Shattrath City is very easy. Instead, take the main elevator from the Terrace of Light and dodge past the NPCs and the Inn to get to the tunnel.
The main Scryer's Tier elevator is one of the best places in the game to get the achievement. Jumping off the elevator at its highest point and landing on the floor of the Terrace of Light (not the bridge) will get you the achievement.
Before the destruction of Shattrath the Scryer's Tier was the Shattrath Residential District, where the draenei of the city lived.