Relative adverbs: WHERE, WHEN, WHY

The relative adverb where is used after nouns referring to places:

The house where Mozart was born is now a museum. (defining relative clause)
I flew to Prague, where I had to catch another plane to Oslo.
 (non-defining relative clause)

The relative adverb when is used after nouns referring to times and dates:

I can’t remember a time when I was so happy. (defining relative clause) 
The most stressful day of the week is Monday, when people go back to work.
 (non-defining relative clause)

The relative adverb why is used after reason:

The reason why I didn’t call you is that I’ve lost your phone number. (only in defining relative clauses)

Grammar quotes
Christmas is a time when you get homesick — even when you’re home.

– Carol Nelson

The only place where success comes before work is in the dictionary.

– Donald Kendall