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