The health center at my university is pretty awesome.
It provides free STI testing days throughout the year. Instead of making an appointment, students and non-students alike can just walk in, check in, and wait their turn, as it's run on a first-come, first-served basis. This particular event was for rapid HIV testing, where HIV results are given within just 10-15 minutes.
I visit my gynecologist annually, but I've never gone specifically to get tested for STIs/HIV. I attended this event curious about what the entire process was like.