Crater

• The location of the crater can be seen on Rousseau's map (e.g. here)
• Area passed by Rousseau, Kate, Locke, Jack, Hurley and Arzt in S01E23 on their way to the Black Rock (see screenshots)
• Area passed by Charlie and Sayid in S01E24 on their way to get back Aaron
• Probably the same location as the "unpassable area" (see Unpassable coast area)
• Probably the position of Desmond's boat
• Edit (04/15/07): The place seen in S03E16 where Juliet talks to Ben about her sister seems to be in a similar terrain (see 4th screenshot). Thanks to Kimeee for alerting me to this