We will be arriving in Terminal 3, LHR on Thursday, July 25th at 9:15 am. We have hotel reservations at the Holiday Inn Heathrow Ariel. Our plan is to go to the hotel upon arrival and hopefully get an early check-in. I have inquired with the hotel about early check-in and was told to check the day prior to the trip. If early check-in isn't available we plan to leave our luggage at the desk and head into London for the day. We leave on a cruise out of Southampton the next afternoon. They hotel says they have transportation from the airport to the hotel so I think that is taken care of; however, I am confused about taking a train (is that the tube...the underground?) or a bus into London. Should we get a ticket in advance...purchase an Oyster card? We have found great suggestions for walking tours we can take on our own while in the city so that is what we plan to do while there but we are just confused on how to get there. Also, what is recommended to get us to the Southampton port on Friday for the cruise. Should we go back to LHR and get transportation from there or try to find something from the hotel. We will be two couples with quite a bit of luggage.Thanks for help/suggestions.