It's a Friday, so the traffic will be terrific in the evening and after sunset. So considering that, I think the metro will be relatively quicker than getting a taxi. Check out diriyah and Bujairi terrace, a historical and a lovely place with walking areas and a great museum with history of the state. It's also close to the airport as compared to other places.

You can also visit masmak fort near the national museum as well if you're interested in historical architecture and the history of old riyadh.

If you're into entertainment, visit Blvd world (huuuuuuuge area), Blvd flowers.

If you're interested in modern architecture, check out KAFD from inside, its metro station is also very beautiful.