Dramatic, varied and remarkably beautiful, the north's great highlight is the Yumthang Valley, though required permits and rushed tours can make a visit more stressful and less rewarding than it need be. For Indian citizens, a second great attraction is crag-rimmed Gurudongmar Lake but it's out of bounds to foreigners, who must stop short at Tsopta (or even Lachen if full regulations are enforced).
To visit the north at a slower pace, it's very sensible to start by heading to Mangan or one of the delightful Lepcha villages of nearby Dzongu. Organising a trip further north from there, rather than as one long slog from Gangtok, can transform your appreciation of the Far North. And once you reach timeless, undeveloped Dzongu, you might well find it is an area you want to linger.