The Ruins of Lordaeron
The Ruins of Lordaeron is all that remains of the City of Lordaeron, the great capital city of the Alliance. Now it serves as nothing more than a sad reminder of the power of the Scourge. The area is literally haunted by the final tragic events that led to the death of King Terenas and the city's destruction.
To this day you can still hear the moments before King Terenas' death; hushed whispers in the courtyard, the clanging of bells in the entryway, the faint cheer echoing the welcome of Prince Arthas, and the murmur of voices in the throne room. One such sentence that is uttered says " This kingdom shall fall, and from the ashes shall arise a new order that will shake the very foundations of the world." — Arthas after slaying his father, and proclaiming the Scourge's invasion and victory over Lordaeron. If you can detect invisibility, you will see the ghosts of the citizens of Lordaeron still haunting the castle's courtyard. Beneath the ruins now lies the Forsaken capital city — the Undercity, where the dark queen prepares to reclaim her lost lands to the east.
The lands outside the ruins are no longer full of cheerful people enjoying the sun, but with demons such as Darkhounds and Duskbats and the Scourge lurking nearby at the borders of the Plaguelands.
There is also a new section of this zone holding an Orb of Translocation that connects the Undercity to the blood elf capital of Silvermoon for those with the Burning Crusade expansion.
King Terenas' Tomb
It is unknown who constructed the memorial to Terenas. It's possible that some Forsaken, feeling some residual loyalty to Lordaeron did it. It could also have been the members of the Silver Hand from when they retrieved Terenas' body. Another possibility is that the remaining Alliance forces in Lordaeron under Garithos erected the memorial during the short time that they controlled Capital City before Sylvanas took control.
It is also unclear what (if anything) the tomb actually contains, since Terenas was cremated and his ashes were scattered by the wind.