"U.S. citizens coming to Lebanon for tourism routinely receive a one-month visa on arrival at Beirut International Airport." (U.S. Department of State) Also note that passports have to be valid for at least 90 days when entering Lebanon and should have no Israeli stamps or visas.
Consider going to a travel clinic or seeing your primary care physician to ensure necessary vaccinations (if any) are given and to ask for any medications that you could bring in case you get sick (stomach ache, headache etc.).
While most places accept credit card, there are many that don't so we recommend bringing cash. No need to convert (USD is accepted everywhere), but having smaller bills can be helpful.
Most major U.S. carriers provide data roaming services in Lebanon, often through international plans or daily passes that can include data, calls, and texts (this is what we usually do, but check with you provider first). Alternatively, consider purchasing an eSIM online before your trip.
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The local voltage is 220V, so you’ll likely need a converter to accommodate this voltage if your device doesn't. Also, since hotels may use different outlets, we recommend a multi-plug adaptor. Common plug types here are A, B, C, D, and G.