Works well with PLA and can add depth by adding other materials at various temperatures.

I really like doing this about every 6 months, it's nice to remember what you were printing by looking at the scrap and half melted prints

You will need -

An oven
Baking tray
Aluminium foil (Alternatively reuse an old aluminium foil tray from pies etc.)
Scrap bits of PLA and any failed prints you don't want to keep
Beer / wine - (to help with artistic inspiration)

Lay the Aluminium foil on the tray and place your largest scrap parts onto it, don't space them too much apart as they will produce a smaller pool of plastic than you would think.

Optionally use some filament to make a round or shaped outer ring to keep all the plastic in if you want a nice shape. (PLA Pizza Anyone?)

Pop it in the oven, heat up to 210 Degrees C for about 15 mins

Then scatter on the smaller parts and heat at whatever temperature you like - 160 Degrees will make things go soft and still keep some shape of what they once were.

It's also quite interesting to throw in some ABS parts as they shrink, distort and go soft creating a more 3D sculpture. 

Keep an eye on the cooking, and remove when you have the desired effect, leave to cool for a few mins and then you can trim the foil and PLA to size (wear oven gloves, if you handle it HOT!) you can form it around shapes, bottles, plates etc. or cut out butterfly shapes if you like. You should have about 5 mins cutting time, or pop it back in the oven to make it soft again.

I hope some of you try it, it's good fun and you may just make a masterpiece.