In Warcraft III: The Frozen Throne, it was described as lying within the frozen peak at the center of the valley in Icecrown, and indeed we actually got to see said peak during the cutscene and the mission. The exact description of the original Throne Chamber before its destruction has differed in four sources. Original Throne Chamber Description and Speculation The Spire: stairway to the Frozen Throne as seen in Wrath of the Lich King. World of Warcraft: Wrath of the Lich King Fail:Spire.jpg "Frozen Throne" now most nearly means the remnants of the crystal that Arthas physically sits upon, as an actual throne. Illidan again failed, and Arthas smashed the Throne - releasing Ner'zhul's spirit and forcing the two to merge into the new Lich King. Kil'jaeden ordered a second attempt and so Illidan, along with his enemies-turned-servants the Blood Elves and Lady Vashj with her Naga, personally invaded Icecrown so that Illidan could smash the Throne in person. The intervention of his brother Malfurion, his former jailer Maiev Shadowsong, and Prince Kael'thas stopped Illidan from succeeding, and he fled. Illidan and his Summoners used the Eye, combined with Dalaran's natural magical energies, to send devastating earthquakes to destroy Icecrown and the Frozen Throne. Illidan Stormrage was charged by Kil'jaeden with destroying it, and to this end recovered the Eye of Sargeras and brought it to Dalaran. The harsh entry into Azerothian airspace and the impact with the glacier greatly reduced its size. Kil'jaeden crafted the original from ice in the Twisting Nether (which was massive - probably about the size of a decent castle) to house Ner'zhul's (now the Lich King's) soul.
The term "Frozen Throne" literally applies to this crystal, about the size of a tauren in full armor. From the confines of the Frozen Throne, Ner'zhul began to reach out his vast consciousness and touch the minds of Northrend's native inhabitants. The frozen crystal, warped and scarred by its violent descent, came to resemble a throne, and Ner'zhul's vengeful spirit soon stirred within it. When Kil'jaeden cast Ner'zhul's icy cask back into the world of Azeroth, the hardened crystal streaked across the night sky and smashed into the desolate arctic continent of Northrend, burying itself deep within the Icecrown glacier. Image of the Frozen Throne at Icecrown Citadel from Lands of Mystery. The Lich King on the Frozen Throne Fail:Icecrown citadel.jpg
Bridges of pale blue, translucent energy stretch from the obelisk platforms to the Frozen Throne. Four stone obelisks carved with runes of powerful magic surround the Frozen Throne.
The Lich King sits on the Frozen Throne at the bottom of the rift, inside of the Icecrown Citadel. After he shattered the top of the throne, the remnants now serve as the actual physical throne of the new Lich King created from the fusion of the souls of Arthas and Ner'zhul. Arthas climbed the steps of the throne on his way to the Lich King. The Frozen Throne (aka Throne Chamber or Lich King's Throne Chamber) was the receptacle of the soul of the Elder Shaman Ner'zhul following his transformation into the dreaded Lich King.