The latest kit in the Superquick range is this superbly adaptable and versatile pair of arches. In each kit you get two arch spaces that you can do lots with. Included in the kit is the option to inset the arches - with or without the unit fronts - you could create a retaining wall, either vertical or sloped - you also have the option of opening this up into a tunnel entrance or even a bridge. This kit includes instructions and will need gluing to complete.
The Deluxe Rocket Card Glue AD-67 is ideal for this kit.