The amount of things to do and see in Berlin is overwhelming - especially as the majority of travellers only come for a weekend.
Most tourists have a bit of an idea of what they want to see in the city before they arrive, which will inevitably include the Big Hitters like the Reichstag, the Museum Island and the Brandenburger Tor (Gate).
But of course there's way more beyond these sights, and other visitors might equally like to avoid the "tourist traps" and concentrate on a "secondary" strata of sights - many of which in fact equal the big names for thrills or cultural value and/or will appeal more to niche tastes.
Whatever your preferences, I'd recommend looking into one of the official Visitor Cards, which have a range (seven in total) of discounted options from two-day weekend visitors to five-day tours for solo travellers as well as those travelling with partner or families. The Berlin WelcomeCard Museum Island, for example, gives free access to the museums on the Museum Island.
You can find out more about these cards and their costs here: http://tourist.visitberlin.de/en/welcomecard/the-berlin-welcomecard?tid=...
How I’ve picked my things to do:
My selection of Things To Do focuses mainly on the city's cultural and historical must-sees - the Reichstag, Museum Island, Brandenburger Tor (Gate) - as well as some of the major sights that deal with the city's darker history, such as the Jewish (Jüdisches) Museum and the Holocaust Memorial.
There are so many things to see in Berlin, I believe it's best to begin with these and remain open to other options and suggestions as you explore the city. To that end I've also included suggestions for main (but not necessarily primary) sights like the Neue Nationalgalerie and the Hamburger Bahnhof as well as a couple of walking and segway tour options, which enable visitors to move around the city more quickly and see more.
I've done my best to come up with suggestions that suit all types of visitor to the city, from families and history lovers to romantic couples and globetrotting backpackers.