The Phurba.
The Phurba, also referred to as "The Dagger" by many of the main characters, is an artifact that Nathan Drake found in Uncharted 2: Among Thieves. It is a knife with three blades, referred to as "a golden passport to Shambhala" by Marco Polo in one of his journal entries. It is also the icon seen on the screen during load times.
Story
After finding the resting place of the sailors of the Lost Fleet of Marco Polo, Nathan Drake, Victor Sullivan, and Chloe Frazer searched it and not only found a map that lead to a temple in Nepal that would reveal the location of Shambhala, but they also found a phurba, a golden dagger traditionally used to clear away spiritual obstacles from one's life.
Eventually, Drake managed to link up with Chloe in the Nepalese city, and during a discussion with her noticed that there was a symbol on the phurba that looked exactly the same as a symbol on an archway nearby. Postulating that the temple that held the location of Shambhala had this symbol displayed on it, they planned to climb a nearby hotel to gain a better vantage point and (hopefully) "spot our needle in the haystack."
Nate uses the Phurba as a key to open the gates of Shambhala.
After ascending the hotel, they spot the right temple and then they are chased by many of Lazarevic's mercenaries (including a helicopter). Along the way, the encounter Elena and Jeff, who were tracking Lazarevic down for NATO and leave them to guard the temple front entrance.
Drake and Chloe descended into the depths of the temple. The phurba dagger is used as a key to open special doors in the temple, and ultimately, the gate of Shambala in Chapter 24 - The Road to Shambhala.
Trivia
- The phurba dagger and stand are part of the limited Uncharted 2 Fortune Hunter Edition.
- The phurba dagger can be seen in the hand of one of the two giant statues of the Ice Cave
- It can be assumed that the phurba was destroyed, as after it opened the gate to Shambahla, the gate descended into the floor with the dagger still in its 'lock'.
- The dagger is never used as any kind of weapon, but it is used to threaten Harry Flynn when Lazarevic feels he "clearly hired the wrong man for the job".
- Even though the phurba was used by Marco Polo to get in to Shambala, he got it back. This is a plot hole, as it appears to be gone when Nate uses it.
The Phurba is one of the icons used in the Uncharted series to indicate the loading screen. The others are the Spanish gold coin (Drake's Fortune), Sir Francis Drake's Ring (Drake's Deception) and Henry Avery's initiation coin (A Thief's End).