Playing on Windows
Crystal Towers 2 comes as a ZIP without an installer. Just extract the contents (including the data and music folders) to anywhere on your hard drive and run the EXE file. Saves will be stored in your Application Data or AppData folder, under "Crystal Towers 2 SE".
Playing on Linux
The game should work under WINE. If you get a message about StringReplace.mfx, try downloading msvcp60.dll.
Playing on a Mac
Crystal Towers 2 has been confirmed to work under Parallels!
Continuing saves from the free version
If you buy the full game, you'll be able to load your save from the free edition and continue with it - the two versions will look for save files in the same place. Once you've loaded your save using the full game, you won't be able to go back to it in the free version.
Is there a Crystal Towers 1?
Yes, but I made it in 2004 and it's rubbish. See for yourself!