"Walking is boring."

Translation: Chodzenie jest nudne.

[jan583285]

Thanks

[EdwardKeat3]

I would have thought that Chodzenie to nudne would have also been OK.

[Jellei]

In an "X is Y" sentence, you can only translate it using the construction with 'to' if Y is a noun phrase.

So for example "Chodzenie to nudna czynność" (Walking is a boring activity) is correct.

But "Chodzenie to nudne" is wrong, because after 'to' you only have an adjective.

See here: https://www.duolingo.com/comment/1637316 - especially Part 3. The gerund "chodzenie" is still just a noun, so it doesn't complicate anything further.