Not far from Feodosia is the famous Karagag Dolphinarium. You can take a bus trip (about 30-40 min) to it.
At the time I've been there it did not impressed me - high prices, bad conditions for visitors and habitants - dolphins. Nothing to compare with "Utrizh" Dolphinarium in Yalta or Sochi. I hope something changed since that time ;-(
Do not miss old walls of Genoese and later Turkish fortress - Kafa. There are several towers (partially ruined) and an old well. Well is an object of note as Crimea peninsular is scanty in water resourses - no springs, no rivers...
Feodosia is the place were the most famous painter of sea-scapes in the world lived and worked. There is a house-museum of Aivazovsky with big art gallery in the center of the town.
Worth to visit.
Nature of Crimea is unforgetable.
Fondest memory: This is Karadag mountain. You will see it if you will go to dolphinarium and bio-station.