Swollen knee. Super swollen but no other symptoms. Doesn't even hurt, not red, don't remember banging it or twisting it. What do I do?

It Depends. On what is causing the inflammation in the knee. Common causes include trauma, infection, inflammatory arthritis (gout, pseudogout, ra), meniscal tears, arthritis, and other ligament/tendon tears. A thorough physical examination and x-rays by your internist or orthopaedic surgeon can help narrow down the differential.
Get checked. There are many no. Traumatic things that can cause knee swelling. You should get it checked because significant swelling is not normal. I don't want to just speculate as some things are benign and others are not. Consider a rheumatologist consultation. A good history, blood tests, and possibly a joint fluid removal for inspection are probably the best first steps.