Celle is small, but the biggest city between Hamburg and Hannover (well, there is nothing much else in between 😉 ). It’s a really scenic place with many old buildings from the 16th century located in the old town of Celle. Since there was only one big bomb attack in WW2 most of the buildings are still in original shape.
Celle is really worth a visit. We visited on a sunny day, which probably is (always?!) better. Two or three weeks before we’ve been there on a rainy day, which was a bit disappointing due to empty streets and grey sky.