In May, me and other half will be stopping for the night in Gravesend prior to our Eurostar the following day. To fill the time in after driving there, we want to get the train into London (on the Javelin, that bit is for me). Now i have looked at National Rail using 2 Adults with Two Together Railcard, in off peak hours, and one of the options is 'With Travelcard'. Does this mean we can use the Underground too when in London, all for £26.30? Also, is it train specific in to and back out of London?