Learn Russian: Эта башня — самое старое здание в городе. - This tower is the oldest building in the city.

Even though the sentence starts with the feminine noun башня (tower), the adjectives самое старое belong directly to the word здание (building). Because здание is a neuter noun, the words describing it must also take the neuter endings (-ое).

How do we form the superlative ("the oldest") in this sentence?

To say "the most" or add "-est" to an adjective, Russian frequently uses a form of the word самый followed by the regular adjective. Both words have to match the gender, case, and number of the noun they describe. Since здание is neuter nominative, we use the neuter forms for both words: самое + старое.

Why is there a long dash (—) in the middle of this sentence?

The dash acts like an equal sign. In Russian, the present tense forms of the verb "to be" (am, is, are) are almost always skipped. When you connect a noun subject (башня) to another noun describing what it is (здание), you usually put a dash in place of the missing "is".

Why does the sentence end with в городе instead of в город?