Over the last few years, I've started walking along the canals of Britain. So far, I've walked the complete length of the following;
Shropshire Union (main line E' Port - Wolverhampton & Middlewich branch)
Bridgewater Canal
Leeds - Liverpool (including Rufford branch)
Huddersfield Narrow & Broad
Ashton (Manchester - Ashton u Lyne)
Worcester & Birmingham
BCN - from Gas Street basin Birmingham to the start of the Shropshire Union.
Currently walking sections of the Rochdale canal. Oh, my dad comes along with me & he's 91 years old - he can still walk 4-5 miles a go!
I've always found the canal walks to be very invigorating. There's also quite a lot of historical interest too.
Yorkie - most of the towpath on the Leeds-Liverpool is in reasonable condition for cycling. Certainly from Leeds almost as far as Steeton, it's excellent though it's a bit patchy after that.