Here is the full list of all 20 Spelunky achievements. It takes around 100-120 hours to unlock all of the achievements on Windows.
Complete the game with at least two players alive. No shortcuts.
Rescue all 16 hidden characters.
Play Adventure Mode 1000 times.
Complete 100% of the journal.
Complete the game without collecting any treasure. No shortcuts.
Complete the game the hard way.
Complete the game.
Complete the game without using shortcuts.
Complete the game in under 8 minutes. No shortcuts.
Obtain 500,000 gold.
Rescue 10 or more damsels in one game.
Kill 12 or more shopkeepers in one game.
Reach the City of Gold.
Reach the Temple.
Complete 50% of the journal.
Obtain the Ankh.
Win the kapala from Kali.
Reach the Ice Caves.
Reach the Jungle.
Beat the Tutorial.