The Ankh is one of the most useful items in the game, capable of resurrecting the Spelunker if he dies.
It is always recommended to purchase it, though it can also be stolen at great risk.
The Ankh will resurrect you whenever you die, spawning you at the entrance of the current level with four hearts, along with all your money and items, but you will lose anything you were holding in your hands and on your back unless you died by suicide.
The Ankh will shatter once it is used, so will only save you the one time. Only one can be bought in each game.
Although this power probably makes the Ankh one of the most desirable items in the game, you will most likely have to squander the Ankh before it is needed in order to reach the City of Gold.
The Ankh's true purpose is to use in conjunction with the Moai in
the Ice Caves in order to obtain the next artifact, the Hedjet.
Dying within a certain distance of the Moai will result in you being resurrected not at the level entrance as you usually would, but inside the mysterious statue where you will find the Hedjet and a secret level exit.
For this to work, and should avoid using a bomb, due to the risk of aftershock effect killing you again as soon as you respawn.
The best method of resurrecting safely is to simply press ESC+F1.
If you are currently wanted by the Shopkeepers, you may wish to be in sight of the Moai when killing yourself, otherwise a shopkeeper may appear inside the Moai with you.
Should you decide to bypass the City of Gold and keep the Ankh as insurance, you must still avoid lava in the Temple. Falling in will melt the Ankh before it can revive you, preventing you from being resurrected.
The Ankh is an Egyptian symbol representing eternal life - appropriate for an artifact that can raise the dead.