Learn Polish: Cyrk to takie imponujące widowisko! - The circus is such an impressive spectacle!

We use takie (such) because it modifies the entire noun phrase imponujące widowisko (impressive spectacle). If you were modifying just an adjective or adverb, you would use the adverb tak (so), for example: Ten cyrk jest tak imponujący! (This circus is so impressive!).

Since cyrk is masculine, why are takie and imponujące in the neuter form?

The words takie and imponujące are describing the noun widowisko (spectacle), which is a neuter noun ending in -o. They must agree with the noun they directly modify in the phrase, not the main subject of the sentence (cyrk).

Could I use jest instead of to in this sentence?

Yes, but it changes the grammar. When you use to to connect two nouns, both stay in the nominative (dictionary) case. If you use the verb jest, the second part must switch to the instrumental case: Cyrk jest takim imponującym widowiskiem!

The word imponujące ends in -ące. Is this a special type of adjective?