This can turn into a nice topic. For me it's easy. Crusaders-Sharks at Twickenham last month. It was huge! I bought tickets, asked a friend to come along, got on the ferry from Hoek van Holland to Harwich, drove all the way to Twickers and we arrived at 9 in the morning, 7 hours before the match.
We took the train to Waterloo Station and toured London for a couple of hours before returning. When we got to the stadium, it was massive. It was not sold out, but still... Seeing the Sharks play so close to home was awesome. We lost 44-28 but it was so much more memorable than for instance England-South Africa in November.