RAR files are compressed archives. If the source is unknown, these are often used to distribute malware or unwanted software (like adware redirects (BleepingComputer)).
Depending on what you are looking for, the "topic" might be one of the following: 🚆 Federal Railroad Regulations (HOS)
It appears in "Snowflake" memo releases from the Donald Rumsfeld era (Bates range 52910-53409). These files often cover historical military policy and senate inquiries (ESD.whs.mil).
If you found a file named on a forum or a file-sharing site:
To help you better, could you tell me or what subject (like gaming, law, or engineering) you were researching? I can then find the specific "interesting guide" you're after.