While looking for more information on the fort at Gajendragarh, I chanced upon a blog post that referred to two more forts around Gajendragarh.
One has to take the Gudlur route from Aihole, which is approx 30 kms and further onwards it is 22 kms one comes into Gajendragarh one of the massive forts. There two more fortifications enroute to this fort along with a Kalkakaleswar temple.
The area turned out have six more fortifications. Looking at the size and shape of the fortifications, I am inclined towards these being sarais or caravan stations than forts.
The fortifications between Aihole and Gajendragarh
The northernmost fortification overlooks Aihole. The remaining five are concentrated around Gudur.
Forts around Gudur

Co-ordinates of each fortification:
Wankandrug or Vakkandurg: 15.9155656,75.8296537
Chikanal: 15.943354,75.8870852
Gudur: 15.9373267,75.9168631
Kellur/Kelur: 15.9751329,75.9067297
Mangalgud: 15.9755868,75.8774292
Aihole: 16.0171395,75.883998
To view these, just input the two numbers as it is into the Search box on maps.google.com.