Do you know directions in London - specifically to & from Croydon?

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We're going to be staying just southwest of South Croydon in a few weeks time and it's very confusing. The hotel's website states a bus operates from the hotel at request Monday through Friday to Croydon town center. I'm assuming for bus/train service since the Tube doesn't run in that area. That trip takes 10 minutes. We don't know how long of a trip it would take from that town center to London or specifically, to the O2. My husband is seriously considering renting a car, but then I found a page on "congestion charge" and car parks and now we're more than just a little confused. It's nerve wracking enough when you visit a new, large city and you're not sure where you're going - but add to that the fact that you're in a country you've never been in before! I've been searching the public transportation sites to no avail. The London train system website won't let me use the hotel's address. So I've been unable to get a route. If you're familiar with this area, please help! Thanks!