6-й відмінок (місцевий): прикметники

In English an adjective never moves: a new house, in a new house, about the new house. In Czech the adjective follows its noun into every case. Once a preposition like v, na, o, po or při has put the noun into the 6th case (the locative), the adjective in front of it has to change too: nový dům (a new house), but v novém domě (in a new house).

The endings

Czech adjectives come in two families. Hard adjectives end in -ý, -á, -é in the dictionary (nový, malý, český); soft ones end in -í for every gender (cizí - foreign, jarní - spring, moderní).

Two things make this smaller than it looks. Masculine and neuter share one ending, so there are really only two shapes per family. And soft feminine adjectives do not change at all: moderní kavárna, v moderní kavárně.

Czech places you will say this with

• Orloj je na Staroměstském náměstí. - The astronomical clock is on Old Town Square.
• Byli jsme v Českém Krumlově. - We were in Český Krumlov.
• Bydlíme v malém bytě na Žižkově. - We live in a small flat in Žižkov.
• Mluvíme o české historii. - We are talking about Czech history.

Place names behave like any other phrase: Český Krumlov becomes v Českém Krumlově, Václavské náměstí becomes na Václavském náměstí. The whole name declines, not just the last word.

The trap: neuter -é is not locative -é

English speakers spot the -é in malé město (a small town, the dictionary form) and think the job is done. It is not: the neuter locative needs the -m as well, v malém městě. So -é on its own after v or na means a feminine noun: ve staré škole, but o starém domě. A quick check before you speak: is the noun feminine? Then no -m. Anything else? Then -m.

The other habit to drop is leaving the adjective in its dictionary form because English would. *v nový dům sounds to a Czech roughly like "in a house new" sounds to you: understandable, and plainly foreign.