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.
Complete the game without collecting any treasure. No shortcuts.
Complete the game in under 8 minutes. No shortcuts.
Kill 12 or more shopkeepers in one game.
Obtain 500,000 gold.
Play Adventure Mode 1000 times.
Complete 100% of the journal.
Complete the game the hard way.
Rescue all 16 hidden characters.
Complete the game without using shortcuts.
Reach the City of Gold.
Win the kapala from Kali.
Rescue 10 or more damsels in one game.
Complete the game.
Obtain the Ankh.
Reach the Temple.
Complete 50% of the journal.
Reach the Ice Caves.
Reach the Jungle.
Beat the Tutorial.