Are there any diseases i can get from walking barefoot in the shower at the fitness center?

Atheletes foot: Or other fungal infections are common in such areas.

Warts, athletes foot: In addition to athlete's foot - which is a fungal infection - people can pick up plantar warts, which are caused by viruses. This is how plantar warts are commonly passed among family members. If i were you, i'd always use flip-flops in the fitness center shower!