Defining relative clauses relating to places and times: 
preposition + which / where / when

When we make relative clauses that refer to times and places, we sometimes use the relative pronouns 'where' and 'when'; but sometimes we use 'which' or 'that':

                  We want a house that (which)  has a large garden.
                  The house has a large garden where you can sunbathe in the summer.
                  Christmas is a time when many people celebrate.
                  It was a day which I will always remember.

This often confuses students. When should we use 'when' or 'where', and when should we use 'which' or 'that'?

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Let's look at some simple statements about places.
When a place is an object, it usually comes directly after the verb:

	(1) 	I bought a house.

But sometimes we make statements about places that need a preposition:

	(2) 	I live in a house.

Other prepositions are sometimes used for places:

		We stayed at a hotel.
		She lives on a small island.
		We went to a beach.

When we make a relative clause with a place or time as a direct object with no preposition - as in example (1) above - we use the relative pronouns which (or that)

	The house which I bought. 
	Or we can omit the relative pronoun as it is the object of the clause:
	The house I bought.

When we make a relative clause with a preposition + place phrase, we can use
a preposition + which, or where. 

	a	The house in which I live
	b	The house where I live

In spoken English, 'b' is more common. 'The house in which I live', is rather formal and would normally be used in writing.

However, in  spoken English, when we use preposition + which, we often put the preposition at the end of the sentence. This is less formal-sounding:

	c	The house which I live in.

Examples

(1) 	[Basic idea: I stayed at a hotel]
	Less formal / spoken	
		The hotel where I stayed.
		The hotel which I stayed at.

	More formal / written
		The hotel at which I stayed.

(2) 	[Basic idea: she lives on a small island]
	Less formal / spoken	
		The small island where she lives.
		The small island which she lives on.

	More formal / written
		The small island on which she lives.

(3) 	[Basic idea: we went to a beach]
	Less formal / spoken	
		The beach where we went.
		The beach which we went to.

	More formal / written
		The beach to which we went.

Remember, it is possible to omit the relative pronoun 'which' (or 'that')  when it is the object of the relative clause. So in the above examples the following are possible:

	(1)	The hotel I stayed at.
	(2)	The island she lives on.
	(3)	The beach we went to.

Example with times:

	[Basic idea: I was born on  a day]
	The day on which I was born. (More formal / written)
	The day when I was born.
	The day which I was born on.
	The day I was born on.