St Nikolai church was the world’s tallest building from 1874 to 1876, and it remains Hamburg’s second-tallest structure (after the TV tower). Mostly destroyed in WWII, it is now called Mahnmal St-Nikolai. You can take a glass lift up to a 76.3m-high viewing platform inside the surviving spire for views of Hamburg's centre, put into context of the wartime destruction. The crypt houses an unflinching underground exhibit on the horrors of war.
The museum's exhibition focuses on three events in World War II: the German bombing of Coventry in 1940; the German destruction of Warsaw and Operation Gomorrha; and the combined British and American bombing of Hamburg over three days and nights in 1943 that killed 35,000 and incinerated much of the centre.
Note that St-Nikolai remains open despite any scaffolding for reconstruction.
A new evening opening time was trialled in the summer of 2018, with the tower staying open until 10pm for four to six evenings a month. The Hamburg panorama, bathed in the light of early evening, is pretty special, so we hope they extend the trial – check the website.