Most Russian cities with a kremlin began as a prince's fort that grew a town. Novgorod worked the other way round. It was a merchant city that in 1136 sent its prince away, started choosing and dismissing princes by popular assembly, and traded with the Hanseatic League through a German trading post called the Peterhof. By the 14th century it was one of the largest cities in Europe, and in 1478 Moscow's Ivan III swallowed it. The city you walk through now was also flattened: the occupation of 1941-44 left its famous monuments in ruins. Almost everything here has been put back.
It's a small, calm city of about 224,000 people on the Volkhov river, a few kilometers below Lake Ilmen, and it rewards slow looking. There's one great church interior (St Sophia), one very good museum of icons and archaeology, a handful of 14th-century frescoes, and an open-air museum of wooden churches. Three days is the right length, with no day trip needed. Staraya Russa and Pskov are in the More time section, with a verdict on which is worth the trouble.
Day one is the Kremlin (the Detinets), day two is the south (Nereditsa, Yuriev monastery, Vitoslavlitsy, Lake Ilmen), day three is the Trade Side across the river. Start on a Friday: the Kremlin museums are all open, the small churches (shut Wednesday and Thursday, or Monday and Tuesday) are open on Saturday and Sunday, and Sunday has the 10:00 service at St Sophia. Daylight is short and some sights shut in the cold, and the practical section is blunt about visas, cards and what governments advise for Russia. Pair it with 5 Days in Saint Petersburg or 5 Days in Moscow.