The dome of the Reichstag Building – the seat of the German Parliament.
http://www.bundestag.de/htdocs_e/visits/kuppel/kupp/245686
Visits can be booked online in advance or if you would like a more spontaneous visit you can be at the Service Center which is near the Reichstag in Scheidermasstrasse at 8am for same day tickets. Included in your ticket is the audioguide which gives the history of the Reichstag and describes the sights as you walk the 230 meter pathway to the top.
From the Reichstag Building it is an easy walk to Brandenburg Gate. Here you find sausage stands which makes it a delicious place for a picnic lunch.
From the Brandenburg Gate it is an easy walk to the Holocaust Museum.
Holocaust museum
http://www.visitberlin.de/en/spot/memorial-to-the-murdered-jews-of-europe
The Holocaust Memorial, officially named the Monument to the Murdered Jews in Europe, can be visited at anytime - night or day. There is an information center open 10am-8pm.It covers an area of 19,000 square meters with 2,711 concrete pillars of varying heights.
Walking back toward the Brandenburg Gate turn right and stroll along the beautiful Unter den Linden street toward the Spree River. Once at the river a left turn will take you to Museum Island which is the location of five museums part of the UNESCO list of World Heritage Sites.
Ishtar Gate
Aleppo Room
One of the museums is the Pergamon Museum 9am to 10pm daily
http://www.smb.museum/en/museums-and-institutions/pergamonmuseum/home.html
Under renovation until 2019 some area of the museum are closed but you can still see the south wing with the Market Gate of Miletus, the Ishtar Gate and the Museum of Islamic Art.