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