There is no other human experience that comes close to navigating inside of an Oceanic wave. Although the sport of surfing, as of late, has experienced an unprecedented growth in popularity; few "surfers" persevere through the painful learning curve (and associated injuries) leading to traveling comfortably in the bowels of a breaking wave.
The "cresting" and subsequent "breaking" of an Ocean wave is caused by the topography of the sea floor directly below the ocean swell. "Hollow" waves are caused by an acute variation in ocean floor topography, i.e., moving from deep to much shallower water. These powerful and hollow waves, are sought after by highly experienced "surfers"- termed "tube" or "barrel" riders.
The most basic pursuit of barrel-riding is "bodysurfing". This method (touted by "Purist") requires only the human body and involves swimming at a speed matching the pre-breaking swell. As the "lip" or top of the wave forms and lurches shoreward; the surfer, having now harnessed the power of the wave, maintains a course parallel (more or less) to the shoreline and glides underneath the 'lip". When the "lip" lands causing a complete enclosure, the surfer is in the vortex or "barrel"of the wave, and is "Locked In"; defined as being inside the wave. The time spent riding in the barrel fluctuates wildly, and is subject to a host of variables impossible to enumerate here; e.g., initial size of the swell, composition and/or contour of the sea-floor, competency of the rider, encroachment of the riders path by other ocean goers, etc...
A myriad of other devices (handguns, swimfins, bodyboards, skimboards, surfboards, jetskis; to name a few) are used by human beings in their pursuit if this experience.
Although methods of entry into the barrel are technically different based on what apparatus one is employing, the tactics used to control ones speed while in the barrel, are basically the same. Causing more drag reduces speed (placing appendages etc., in the water) and riding higher and then lower on the wave face in rapid and/or continuous succession (termed "gyrating" or "high-lows") increases speed. The ability to navigate"behind the curtain" is cultivated over years and through tears.
Many "hardcore" Surfers cross-train in other athletic activities, such as Yoga, long distance swimming, martial arts, beach running, under water rock toting, etc,.. in the interest of maintaining their physical stamina.

Things You Will Need

1. If you are over 40- a psychiatric assessment!
2. You may ride in the "barrel" of a wave using a myriad of devices (swim fins, bodyboard, surfboard, jet-ski,) or simply a human body (preferably your own); although I've witnessed dogs get "barreled" on occasion.
3. A wet-suit to prevent hypothermia, if in a less than "tropical" climate.
4. Sunscreen
5. Very hollow waves. Some of the more renowned locations are:
a. Pipeline on the North Shore of Qahu
b. Puerto Escondido in Mexico
c. Numerous reef breaks in Tahiti
d. A secret spot on Lombok, Indonesia
e. Big Rock in La Jolla
f. Padang Padang on Bali, Indonesia
g. Cyclops in Australia
h. Shipsterns in Tasmania
i. A million other places on the globe

It is easy to exhaust ones cognitive capacity, while attempting to articulate the sights, sounds and sensory overload associated with riding in the barrel of a wave. The spectrum of stimuli and emotions extends from re-living my birth, to Neptune pouring 10 Olympic size swimming pools over my head, with the associated impact sounding like a gargantuan cement truck depositing it's contents just a few feet away. Then, there is the ultimate; the precious and most coveted jewel of "barrel" riding experiences- getting "Spit Out". This occurs when the the vortex of the wave has stayed open for enough time to accumulate air within the barrel. As a "tuberider" is poised for exit from the confines of a barrel, the elements accompany him/her in a grand finale of exhalation, a hydro-blown cacophony, if you will; similar to being blasted out your backdoor by a high power garden or fire hose.

Tips & Warnings

There are many hazards in the ocean; some obvious, some not. Always check with local folks and/or Water Safety personnel prior to entering the Ocean. Never remain in the Ocean while you or someone proximal is bleeding; sharks have exemplary olfactory glands. Do not encroach on the space of individuals deemed "Locals" in their aquatic backyard. Many "Locals" possess a deep sense of entitlement they believe warrants the use of physical violence.