Learn Turkish: Gece bisiklet sürmeyi sevmiyorum. - I don't like riding a bike at night.

The verb sevmek (to like) requires its specific object to take the accusative case ending. Here, the thing you don't like is the action of riding. We make the verb sürmek into a noun by adding -me to get sürme (riding). To connect this verbal noun to sevmiyorum, we add the buffer letter -y- and the accusative suffix -i, giving us sürmeyi.

If sürmeyi has an ending, why is bisiklet (bicycle) in its plain form?

Because you are talking about riding bikes in general, not one specific bicycle. In Turkish, general, non-specific objects stay in their bare form. If you wanted to say I don't like riding that specific bike, it would take the accusative case: O bisikleti sürmeyi sevmiyorum.

Why is 'at night' just Gece and not Gecede?

Common parts of the day in Turkish, like gece (night), sabah (morning), and akşam (evening), don't need the locative ending (-de or -da) to mean in the or at. You simply use the plain word as an adverb of time.

How does the negative work in sevmiyorum?