This shrine inside Ueno-kōen was built in honour of Tokugawa Ieyasu, the warlord who unified Japan. Resplendent in gold leaf and ornate details, it dates from 1651 (though it has had recent touch-ups). You can get a pretty good look from outside the gate, if you want to skip the admission fee.
In January and February there is a spectacular peony garden; from mid-September to 30 October the same garden blooms with dahlias. Entry to either is an additional ¥700.