Once you've bought your card online, you can pick it up at any of the locations listed above, but you don’t have to activate it immediately. You can specify a later time if you're not going to use it straight away. And because the cards are valid for 24, 48 and 72 hours, if you activate it at midday you can use it until midday the following day (or two or three days later), so you don’t have to cram all your sightseeing into one day.