General:
* House of Knowledge
* Temple of Learning
* Forge of the Mind
* Cradle of Scholars
* Gate to the Future
More specific:
* Book-Lover's Sanctuary (if focusing on libraries)
* Debate's Arena (if focusing on discussions and arguments)
* Professor's Realm (if focusing on teachers)
* Young Mind's Playground (if focusing on students)
* Career's Launchpad (if focusing on future ambitions)
You can also be more creative and use kennings that reflect a particular type of college, for example:
* Ocean of Art (for an art college)
* Laboratory of Life (for a science college)
* Bard's Academy (for a college of the arts)
* Mountain of Medicine (for a medical college)
Ultimately, the best kenning for "college" will depend on the context and the specific message you want to convey.