The official tours are free so you may as well! Having said that, the lines to join the tours can be long, so you may be better off booking a half-day or full-day tour of Abu Dhabi which includes a visit to the mosque. Official tours take between 45 minutes and an hour and will fill you in on the history, architecture, and religious significance of the mosque. Alternatively, you can pick up an e-guide, which includes audio commentary in Arabic, English, Chinese, German, Italian, Spanish, Portuguese, Urdu, French, Japanese, and Russian. The audio guide covers the internal and external architecture of the mosque as well as the story of Sheikh Zayed, details about Emirati national dress and culture, and information about Arabic calligraphy. The e-guide is free to rent, but you’ll need to leave a form of ID with the service desk as a deposit.