Lisbon has nowhere near the level of rampant graffiti that Athens has, but there is still some creative and impressive street art in the downtown area.
Here's a small sampling from around Bairro Alto, Chiado, Rossio, the Alfama, and Belem:
Travel Advice for Portugal
You can find the latest U.S. Department of State travel advisories and information for Portugal (such as entry visa requirements and vaccination requirements) here.
Health & Vaccinations
The CDC makes country-specific recommendations for vaccinations and health for travelers. You can find their latest information for Portugal here.