No board, no blades, no problem. If you're looking for a sport that lets you do grinds, railslides and backsides - even without a board - hit the street and try some freestyle walking.
Freestyle walking or soaping is a combo of
Soaping can be done using just your regular old sneakers but it's easier if you buy a special pair of soaping shoes. They're fitted with a special, removable plastic grind plate that screws into the bottom of the shoe under the arch of the foot. This roundish plate allows you to smoothly glide down rails or curbsides. The shoes are usually made of leather and have special laces so you can avoid tripping. The downside is they cost about a hundred bucks - but it's worth it if you're going to be doing a lot of soaping.
The great thing about freestyle walking is that you can do it anywhere and the only thing limiting your tricks is your imagination. A flight of stairs, a parking meter, a newspaper box or a garbage dumpster can all become part of your own street obstacle course. Like any sport, just be careful and know what your limits are.