New Kingdom, Dynasty 19, Rameses II; New Kingdom, Dynasty 20, Rameses IX; New Kingdom, Dynasty 18, Amenhotep IV/Akhenaten; New Kingdom, Dynasty 20, Rameses X
By any standard, Tomb 5, the tomb of the sons of Rameses II, is unique. It's the largest tomb ever found in the Valley of the Kings, one of the largest known in Egypt. It's unique in its complex, multi-level plan, and unique too in its function as a royal mausoleum.
The entrance to Tomb 5 was first noted by James Burton in 1825; he was the first European to enter the tomb. But Burton was able to crawl only into the tomb's first nine chambers—the tomb was so filled with debris that he didn't even realize it was decorated. Burton and later visitors concluded that Tomb 5 was simply a small, unused hole in the ground of no archaeological importance at all.
In 1989, however, the Theban Mapping Project relocated the entrance to Tomb 5 and quickly discovered that the tomb was decorated and texts on its walls identified it as the burial place of several sons of Rameses II. Suddenly, it had become a tomb very much worth exploring further.
Over the next six years, they cleared the densely-packed debris from the tomb's first few chambers. They found elegantly carved relief scenes and texts on chamber walls that included the names and titles of at least six royal sons.
Then, in February 1995, they dug a narrow channel through the debris that blocked a doorway at the rear of chamber 3. Instead of leading into a small side chamber, they found a set of corridors over sixty meters long, lined with dozens of small side chambers. Tomb 5 had suddenly become the largest tomb ever found in the valley and it immediately received worldwide attention.
Since 1995, continued excavation has shown that Tomb 5 has at least 130 corridors and chambers. And its symmetrical plan suggests that there could be as many as two hundred chambers, or even more. They found hundreds of thousands of potsherds, hundreds of small objects and many square meters of decorated walls.
The project has been especially concerned with engineering and conservation work in Tomb 5. This unusual tomb demands not only clearing but protection, and much time is devoted to ensuring that it is left in sound condition, its decorated walls cleaned and well preserved.
This means it's going to take many more years before Tomb 5 is completely cleared and conserved. And therefore, it isn't likely to be open to the public for a very long time.
Valley of the Kings, Tomb 5, 6, 18, 19, and 55

Tomb entrances.
New Kingdom, Dynasty 19
Chamber 02: pit

Intact human skeleton.
Corridor 07

Corridor partly cleared of debris; recess with Asar (Osiris) at rear.
Corridor 07: rear wall

Asar (Osiris) carved in high raised relief in recess.
Corridor 11

Partially excavated corridor.
Corridor 13; Gate 13; Corridor 12; Gate 12

View from corridor 13 through gate 13 to corridor 12 and gate 12.
KV5: A Preliminary Report on the Excavation of the Tomb of
the Sons of Rameses II in the Valley of the Kings.