The Idun Online installer is all you need to begin your adventure (3GB)!
Make sure that you patch the client after finishing your installation.
For the direct link, you would need to rightclick and manually use the 'save as function'.
Click one of the links above.
Download the file to your hard drive.
After the download has finished, open the Idun-Ragnarok Online Installer.exe.
Please make sure you don't install Idun-Ragnarok Online on your Desktop, My Documents, or Program Files.
Launch the Game Patcher with administrator privilege.