Carlisle airport itself doesn't really have very much going for it, although the bacon butties ar OK, but the Lakes are definitely worth a flight. Only advice would be to avoid the weekdays as there tends to be a lot of fast, low, grey pointy things which also like the Lakes.
It is lots of fun taking a trip down into the valleys and flying along the lake itself - Bassenthwaite is the nearest to Carlisle and very pleasant to fly down, especially as it is 'open' at either end, so no need to be worried about becoming trapped in a closed valley. Ullswater is also very nice, with a slightly more interesting entry if you come in from the West, scooting down the side of Helvellyn, and Haweswater is a narrow little man-made lake with a submerged village at the southern end and a dam at the other - great fun for dambusting (just beware the house on the dry side of the dam - not that I'd ever suggest breaking the 500' rule).
Personally, I reckon the best flying you can get is over to the west coast of Scotland - it has to be seen to be believed. No written description can do it justice. Oban is a really nice little airport to drop in for a fuel stop, and I'm sure there will be loads of others who will tell you what a thoroughly nice guy Paul Keegan is too. Not much at the airport, but the views are spectacular and there are loads of interesting places to go and see within a short flight form there. Not seen it myself, but there is a pretty viscious whirlpool between Jura and Scarba when the tide is on the turn - makes you think twice about ditching!