I purchased a three-day train ticket this time. The three days don't have to be used consecutively, which makes the itinerary more flexible. You'll receive a QR code by registering your usage dates on the website via the email link. Simply scan the code at the station gate to enter. Please register at least 2 days in advance of your travel date. You'll get one QR code per day, so I registered for 3 different codes. On the first day, I traveled from the airport to Paddington, then to Bristol. On the second day, I visited Bath and Oxford. On the third day, I returned to London from Bristol. I recommend reserving a seat for the journey from Bristol to London, as the train tends to be crowded. The ticket includes one free seat reservation, which I found to be sufficient, as there were plenty of seats on the other train journeys.