Learn Dutch: Het toilet is bij de badkamer. - The toilet is next to the bathroom.

While naast means strictly "next to" or "adjacent", bij is a bit broader and means "near", "at", or "by". Saying the toilet is bij de badkamer implies it belongs with the bathroom or is in that same general area. The English translation captures this practical meaning well.

Why is it het toilet but de badkamer?

Toilet is a neuter noun, so it gets het. Badkamer is a compound word made of bad (bath) and kamer (room). In Dutch, the gender of a compound noun always matches its final part. Since kamer is a de word, the whole word badkamer is too.

I usually hear people say de wc. Is het toilet used differently?

Both mean the same thing and are very common. De wc (pronounced "way-say") is the most standard, everyday term, especially in homes. Het toilet sounds slightly more polite or formal, so you will often see it in restaurants or public buildings.