Everybody's mostly got it right (Close is... the closest!
). The G-Spot is located only a few inches into the vagina (varies from 1-2, to sometimes 3-4 inches in, though about 2 inches in is the norm) and is on the "top" of the vaginal wall (that is, the top is the closest to your clitoris). The G-Spot feels like a small round piece of skin (much like the clitoris, but bigger) that may grow or even "get hard" the closer you get to orgasm while manipulating it. I hope this clears everthing up!