Cant download a map right. Please Help!!

Someone please help me figure out how to download the map "This map just keeps getting bigger". I directly downloaded it and copied it to my desktop and all it showed up as was a Rar file. Help would be greatly appreciated

A RAR file is like a zip folder, it contains files inside that are accessible once you unzip it. If you have a tool like 7-Zip and WinRAR open the rar and place the folder inside in your Minecraft saves folder.

Thank you very much that helped me