If Wimbledon is in full swing, that is a must see!
Even if you just get on the grounds it is spectacular. They have a line for resale tickets for when ticket holders leave for the day and turn in their tickets to Centre Court, Court 1 and others. You can buy them and the small fee goes to charity. That is how I got on to Centre Court. Outer courts have limited seating but most of them are first come/first serve.
https://www.greenandpurple.com/how-to-buy-returned-wimbledon-tickets-at-the-resale-kiosk