Germany

Reasons to go:

Schwerbelastungskörper (The Heavy Body) - a heavy load-bearing body made of solid concrete. It was erected in 1941 to test the load-bearing capability of this area.
Flakturm Humboldthain - the remains of a Second World War anti-aircraft gun blockhouse tower. I’ve heard of guided tours that can take you inside.
Bierpinsel - a fun building.

Still on my to-visit list:

Jewish museum (both the building itself and the museum inside)
KÖNIG Galerie
Stasi Museum (Stasi spying equipment housed in imposing, original HQ of the secret police)
Design Panoptikum (surreal museum of industrial objects)
silent green Kulturquartier (events, art and café in what used to be Berlin’s first crematorium)
Spandau Citadel (old part of Berlin)
Classic-Remise Berlin (vintage cars)
Buchstabenmuseum (collection of abandoned typographic signs)
Monsterkabinett
DDR Watch Tower
House of One (a house of worship that brings a synagogue, a church, and a mosque together under one roof)
tours by Subterranean Berlin
city views from the TV Tower
and all the museums on the Museum Island

Teufelsberg - an 80 metre hill created from 75 million cubic meters of post-Second World War rubble. It covers an unfinished Nazi military-technical college. During the Cold War, it was a US listening station. Now it is a street art gallery. Area is well double-fenced, double check the opening times before heading there. Entrance is not free.
Artpark Tegel - 8 huge murals on 4 buildings; starting from (52.576079, 13.272607) and east from there. Nearby BaliBowls offers ok food.
East Side Gallery - outdoor street art gallery stretching from Park an der Spree (near Berlin Ostbahnhof) to Oberbaumbrücke (Oberbaum Bridge).
Still on my to-visit list: Urban Nation, following Giulia’s guide, Urban Spree (not open on Saturdays?), Haus Schwarzenberg.

Velvet - the world’s most exciting cocktail bar!
Kopps - excellent vegan tasting menu. I’ve not yet tried their cocktail bar.
Tadshikische Teestube - Tajikistan tearoom.
Bamboo Leaf - Vietnamese restaurant. Great mango curry. Don’t miss Kaiser Wilhelm Memorial Church (1890s church damaged in the war) while you are in the area.
Hallesches Haus - nice food in a wonderful setting.
Saravanaa Bhavan Berlin - authentic South Indian food.
Bellboy Bar Berlin - a pretentious cocktail bar inside a Hilton Hotel building. They cherish their dress code. Marian Beke joined their team in 2023, so cocktails will likely improve. You must visit their bathroom - it is an experience, especially during busy times.
Still on my to-try list: FREA (zero-waste vegan restaurant), Fairytale Bar, CODA Dessert Dining, Alaska Bar, Markthalle Neun (indoor market).

Tempelhofer Feld - former airport-turned-public park. Next time I’m planning to shop at Markthalle Neun and bring a picnic here.
Mauerpark - on a Sunday morning this is THE place where Berlin people hangout. Nearby is Café Morgenrot - they used to serve an all-you-can-eat brunch to die for, now I wouldn’t go there for food…but perhaps for the experience of a cafe where “right-wing behavior is not tolerated”.
Treptower Park - a park with a Soviet war memorial.
Still on my to-visit list: Botanical Garden and Botanical Museum, Nature Park Schöneberger Südgelände, Tiergarten, Gardens of the World, Spreepark, Britzer Garten.

BVG Tickets Berlin - one app for all public transport tickets. A 24-hour ticket might not save you money, but allows you to travel through the city worry-free.
Always have cash on hand, surprising amount of “they’ll definitely take cards” places are proudly cash-only.
All museums are free on the first Sunday of every month.
Read about Mietskaserne Tenements before you go, in case you get to stay in one of these buildings.
Berlin is very vegan.