The area behind Kings Cross has recently undergone quite a transformation, Granary Square, and can be an interesting stroll if the weather is good.
There's plenty to see and do in Bloomsbury - the British Museum is spectacular and there are lots of small places like the Charles Dickens museum in his London home. There are lots of interesting old bookshops to browse around. There's an app for your phone which maps all the Blue Plaques in London - you could stroll and look at where the good & great have lived.
If you fancy something more lively, Camden Market is around 15-20 minutes walk north but it does get very, very busy. You can walk along the Regents towpath to get there, which is a super walk.