A group of 4 teenage girls will visit London for two days and want to use a travel card for both days. But a paper travel card is £12 per day and the cap on an Oyster card is about £6.50 for the day.
Only one of the girls has a contactless bank card.

Now is the question, where can you buy such an Oyster card and how do you get your deposit and left over money back after the short visit?