Modern buildings are a great source of reflections, because the exterior is usually clad in glass panels that reflect everything from the sky to other buildings nearby. Old building such as castles and stately homes often have water nearby, in the form or moats or ornamental lakes – if you move in close you can capture a mirror image of the building reflecting in the water. Use a telezoom 
to fill the frame for abstracts and a wideangle for broader views, and remember to focus on the reflection itself rather than the surface containing the reflection.