There are a maximum of 33 Half-Life 2 achievements worth 507
5,082 tracked gamers have this game, 899 have completed it (17.69%)
Discover the hidden singing vortigaunt cave in chapter Water Hazard.
Unlocked by 1,567 tracked gamers (31% - TSA Ratio = 1.79)
Do you have a question about this achievement? Please post it in the Half-Life 2 Forum