In

in a room in a building in a box

in a garden in a town/country in the city centre

in a pool in the sea in a river

• There's no-one in the room / in the building / in the garden.
• What have you got in your hand / in your mouth?
• When we were in Italy, we spent a few days in Venice.
• I have a friend who lives in a small village in the mountains.
• There were some people swimming in the pool / in the sea / in the river.

At

• Who is that man standing at the bus stop / at the door / at the window?
• Turn left at the traffic lights / at the church / at the roundabout / at the junction.
• When we were in Italy, we spent a few days in Venice.
• We have to get off the bus at the next stop.
• When you leave the hotel, please leave your key at reception. (= at the reception desk)

On

• I sat on the floor / on the ground / on the grass / on the beach / on a chair.
• There's a dirty mark on the wall / on the ceiling / on your nose / on your shirt.
• Have you seen the notice on the notice board / on the door?
• You'll find details of TV programmes on page seven (of the newspaper).
• The hotel is on a small island in the middle of a lake.

• There were a lot of people in the shop. It was very crowded.
  Go along this road, then turn left at the shop.
• I'll meet you in the hotel lobby.
  I'll meet you at the entrance to the hotel.

• There is some water in the bottle.
  There is a label on the bottle.

• There is somebody at the door. Shall I go and see who it is?
  There is a notice on the door. It says 'Do not disturb'.