As work continues on the Union Terminal restoration, it's easy to see changes to the front facade. However, lots of work is happening inside and behind the structure as well.

Scroll down to take a look behind the scenes.

Officials are still waiting to hear in June if the project will receive $3.25 million worth of state tax credits. The project has twice been denied and the financial team is starting to feel less optimistic because of strong competition from other projects around the state. The largest issue, they say, is that the museum is still occupied. The Children's Museum remains open during construction. One criteria for state historic tax credits is an empty building.

Should the credits be denied a third time, the project shouldn't suffer. The Cincinnati Museum Center announced in February it sold its federal historic tax credits for nearly $10 million more than expected. Some of that overage could cover any loss in state credits.

Though the Children's Museum remains open, The Woods section will close for several months beginning in August. The ceiling of that section must come down in order to replace aging mechanical and electrical systems.

All of the granite and limestone has been removed from fountain plaza. Eventually the fountain base will be removed as well in order for major roof repairs. The fountain sits above the Children's Museum. The aging basin in which the fountain sits must be removed. Architects are beginning small-scale experiments to determine the best kind of replacement basin.

The original doors are being removed for cleaning. They will be reinstalled. Architects are experimenting with several cleaning methods for various parts of the building such as the metal facings, stone surfaces, and the painted rotunda ceiling.

In the center block above the vent you can see where crews are experimenting with several cleaning techniques including using dry ice. Dirt particles are frozen and then blasted clean with high-powered air.

The insides of the Natural History and Cincinnati History museums are being entirely reconfigured and reconstructed. This space, which used to house the flatboat display adjacent to the Public Landing, will now permanently house the Duke Energy Holiday Trains.

Union Terminal is getting all new electrical and HVAC systems, including 478,0000 pounds of duct work. The reconfiguration also allowed for opening up previously unused spaces, adding 50,000 square feet of additional exhibit space.

One of the biggest unexpected projects has been replacing the drum wall behind the rotunda. Plastic sheeting covers the space behind the main rotunda where a brick wall once stood. Decades of damage necessitated the wall be removed and rebuilt.

This is a reverse view from behind the plastic sheeting above. You can see a portion of old brick drum wall.

Part of the challenge to replacing the drum wall is figuring out how best to engineer a curved brick wall. Here you can see the curved walkway between the rotunda and the now-removed brick wall (at left).