"Institution" and "facility"

Solution 1:

An institution does not refer to a physical structure but rather to an organization, establishment, foundation or society. Any of these may have buildings but the buildings are not the institution itself. You could refer to the building as a structure or in some cases it may be appropriate to refer to them as offices or dormitories. A number of buildings can be referred to as a complex.

Solution 2:

In university environments, different buildings are often referred to using the term "Hall" as a suffix to the building's name. More generally, groups of related buildings on a University campus are often referred to by the term "College," as in 'College of Engineering' or 'College of Health Professions.'

Solution 3:

You could say

There are three institutions in this campus

However as Mark said in his answer, that would typically not be taken to mean three buildings. Rather, that would imply that three different universities all shared the same campus, or possibly that the university had three different departments. Or, it could mean that the university has a hospital and a church on campus, for example. It refers to organizations or groups rather than to *physical buildings.

Merriam Webster defines an Institution in this case as:

an established organization or corporation (as a bank or university) especially of a public character

For a better understanding, see the word institute, which wikipedia defines as:

An institute is a permanent organizational body created for a certain purpose. Often it is a research organization (research institution) created to do research on specific topics. An institute can also be a professional body. In some countries institutes can be part of a university or other institution of higher education, either as a group of departments or an autonomous educational institution without a classic full university status such as a University Institute.

A "Facility" could be a building, but does not have to be. It could be a part of a building, or, it might not even be a building at all. Some other kinds of structures could be called facilities (water facilities, electrical facilities).

If you're really looking to describe buildings, try one of the following:

• structure
• construction
• edifice
• architecture

I got these from a thesaurus... I have to say that none really feel as right as "building" when talking about, well, buildings. :-)