On a clear day, one can see for miles around.
I would say it is one of the five top activities to do while in St. Augustine. The other activities is seeing Castillo De San Marcos, walking historical St. Augustine, seeing the Lightner Museum and taking the Flagler Hotel/college tour. Other activities to do is seeing the Distillery, walking the Bridge of Lions and taking the Victory III scenic boat cruise.
The Lighthouse is 165 feet up built in 1874. It is quite large and there are levels where one can stop and rest.
A nice museum starts the journey—with a large focus on WWII relating to the Coast Guard in the area.
It is that view, though, which is awesome and totally worth your time to visit and explore.