Large lighthouse type structure on the way to Tampa airport on rt 79 near exit 42?

Answer 1

Egmont Key Light
The light at Egmont has stood at the entrance to Tampa Bay since the mid 1800's. It is very likely the oldest structure in the Tampa Bay area to still be utilized for it's original purpose. The light's beacon can be seen from a distance of 15 miles, thanks to it's flashing 140,000 candlepower light. The Egmont light was not automated until 1990, making it one of the last in the country to be converted. Egmont Key is accessible only by boat. Several sightseeing boats ferry visitors to the Key from Pinellas and Manatee county beaches. Egmont is also a popular anchorage for private vessels.

Answer 2

You may be thinking of I-275 north of downtown. It's the old Sulphur Springs water tower.

Answer 3

Thinking anout Bok Tower, maybe.....