As we've diverted from purely talking about NT, just to say, if you join English Heritage, it will get you into the Scottish and Welsh equivalents, half price first year, free after that. A good one also to bear in mind is Historic Houses (HHA), that gets you into lots of privately owned historic houses that you might not otherwise see. We thought it worth paying the roughly £70 odd quid a year for each, as you never know where you might turn up and think, that's interesting, and then you see the price and don't bother. We like the idea of just waving the card and wandering on in !