It is worth 40k. Once obtained, you can take this to Mandrith in Edgeville bank or Nastroth in Lumbridge Castle's courtyard for 40,000 coins. Note: These can be traded, but not in note form.
It is a game where you raise different skills, trade, combat monsters, build items... Just try it, and see whether you like it. The Web site is www.runescape.com. The basic game is free. Paying...