Of a similar bent as cave exploration, the more modern hobby of urban exploration is just as risky, in its own way, but does not present the extensive need for equipment that delving beneath the Earth does. The caves that urban explorers traverse are those made by man as opposed to nature. The often forgotten areas of the city are their destinations, including such places as old sewer systems, dilapidated industrial buildings and abandoned commercial and residential structures. This hobby is not strictly legal and can even be considered a serious trespassing offense when one’s exploration target is say, the old Roman sewer system below the city of Rome. Most of these places are off-limits and owned by some party or another and to be caught can land you some jail time. So, while I cannot officially endorse that people give this hobby a try, I’d say that I, personally, am going to take some time out of my remaining years to pursue it myself.