Papier Mache train tunnels.

I might be wrong here, but I'm guessing that most children have a toy wooden train set at some point in their pre-school years.  Certainly my two nephews and my children do.  C loves his trains.  We started with a figure of eight set up with Thomas the Tank Engine, and Annie and Clarabel the coaches and now have at least seven engines with appropriate tenders for the steamies, and also a variety of trucks and coaches.  The track has grown with the addition of a turn-table bridge, a set from Tesco and a Big Jigs extension set which allows for all sorts of junctions and crossings.  Are you beginning to get the impression that I love building the tracks as much as C does?  C is now capable of putting the track together himself, though he needs help getting the ends to join up; while Bug adores the trains and will happily pick up an engine and drive it around the track for ages (though she's not quite delicate enough yet and this game is invariably followed by wails of despair from big brother as she's sat on the bridge or something).  While big cousin D was staying I thought that making some tunnels for the trains would be a great way to give him some papier mache experience.

I cut up an Amazon box for the bases.

Cut up some cereal boxes and tape them in place curved over on the base to provide the skeleton of the tunnel.  I also made a cave for a toy wolf.

Make the paste with flour and water.  It needs to be pretty gloopy.

Build up the sides of the tunnel to  make hillside type contours using screwed up balls of newspaper dunked in the paste and shaped with your fingers.

Tear up newspaper into squares and strips.  Stick these with the paste all over the outside of the tunnel, making sure they overlap and criss-cross as much as possible.  I've found that the best way to do this is to generously brush paste all over the outside, then stick the strips and squares down all over, followed by another generous coat of paste.  Any bumpy bits or dry bits can be moulded or pasted with your fingers.  Make sure that the whole model is covered by the newspaper, including folding some over the ends of the tunnel and into the inside.  If any is coming over the edge of your base this isn't a problem as it will be trimmed afterwards.  If you are making a cave, then don't forget to add bumpy bits and texture by doing papier mache on the inside too.

It is quite a messy activity, and I strongly recommend a wipe-clean tablecloth or newspaper over your surface and also aprons.

Once you've done a few layers, put them somewhere warm to dry for at least twenty-four hours, preferably longer.

After the models are dry, trim the edges of the base and then paint.  We were aiming for green on the top and black inside the tunnel, but I made the mistake of putting the black out first, so the green was mostly black too by the time it had been well mixed.  

I love papier mache.  As a modelling activity it's hard to beat for versatility, ease of finding equipment, ease of technique and opportunities for getting dirty. The children certainly enjoyed making these models, and D was delighted to take home his very own hand-made tunnel for his trains.