✔ 最佳答案
Hi there,
1) Yes, you can refund the oyster card at ticket counter at any London Underground station. There should not be any admin fees.
2) Buckingham Palace only opens during the summer so it may be worth visiting. London eyes is okay on a good day. But I found the view is better around time for sunset in UK (currently 8-9pm).
St Paul Catherdal - not really worth to visit inside. Perhaps a photo from the outside?
Another place recommend to visit is Greenwich Royal Observatory.
http://www.greenwich-guide.org.uk/observ.htm
You can have a nice view of London from the Observatory.
參考: Myself - Live in UK.