If you are ever in Philadelphia, it is worth a visit to the Morris Arboretum in the Chestnut Hill section of the city.
It is a wonderful garden experience as well as a terrific garden railroad, that winds under shrubs, trees and has many bridges, including one that passes overhead. There must be 8 or 10 trains running at once as well as Hill climbing geared cars.
It is open during warm weather, from approx April to October and then Holiday themed trains running from Thanksgiving until Jan 2nd.
The buildings are constructed of natural materials (pine cones, bark, reeds, branches etc. and are of historical buildings from the Philadelphia area. For the Holidays the houses are decorated with lights, garlands, candles, wreaths,etc.

Package trains

Decorated house

High Bridge