Event horizons are boundries in space-time in wormholes. The event horizon of the Stargate gives the appearance of water. Samantha Carter was amazed to see that the fluctuations in the event horizon were visible and appearing as ripples in water. (Stargate) (SG1: "Children of the Gods")
The event horizons of black holes cannot be viewed by normal perception, as gravity draws light into the event horizon and prevents it from being seen. (SG1: "Singularity", "The Pegasus Project")