This Trolley Bus Paper Model would be a good fit for 25mm – 28mm figures.
paper model
Industrial Terrain Gaming Mat
Top Solitario offers a gaming mat of an industrial landscape. Just download, print, mount and play.
Star Trek Shuttlecraft Galileo Paper Model
The classic Star Trek shuttlecraft Galileo is available as a free paper model.
Paper Model Ruins For Frostgrave
Osprey is supporting their popular Frostgrave rules with some paper model ruins for the game. They could of course also be used for a number of other medieval and fantasy games.
Papercraft Nativity Set
Schweitzer Comics offers a very nice paper model Nativity Set. It’s not quite free, but it is “pay a fair price.”