The wonderful festival returns in late April - early May with a packed schedule of events: http://www.haltwhistlewalkingfestival.org/
If you have not been on one of their day or half day hikes, which are expertly guided, and invariably end near a decent pub or tea shop you are missing out. It is wonderful walking country with parts of the Pennine Way, Hadrians Wall and so many other amazing walks all around. You do not need to be local as tourists come from miles around often on a repeat basis.
Full details on the website but you will want to book ahead.
For my part when I was in Haltwhistle last weekend there was a real sense of excitement not just about the coming walking festival - which goes from strength to strength - but also from the rebirth of the new rebuilt hospital, following on as it does from the new Library.
One project I also popped into was the Whistle Art Stop - which is right in the centre of town. It is a great project that I will write more on when I return there at the end of the month.