In reply to RX-78:
I love the Cheviots, they are bleak and empty, it's my "local" hills but you can often have it to yourself if you go midweek or in an evening. I've had days when I've not seen anyone despite it being glorious weather.
Cheviot and Hedgehope from Langleeford is the classic round but can (is always) be boggy, my preference (as a runner) is clockwise.
Hedgehope can also be done from the other side, and a visit to Linhope spout is nice (though it's probably the busiest bit of the Northumberland National park)
There's lower stuff from Alwinton etc, and if you follow the road to Barrowburn etc it begins to get very empty and feels very remote! There's some river dunking here as well so great on warm day.
https://www.ukhillwalking.com/logbook/r/?i=1284
It's a very different character to the Lakes, maybe more Howgillsy but much lonelier! It's great.
If you can get it, there is a Harveys superwalker map for the national park.