Much like the New Deal, free refills, and ownership of the moon, baseball helped make America the great nation it is today. Salute our national pastime with today’s Groupon: for $15, you get $35 worth of lessons or training-tunnel rentals at Extra Innings in Miamisburg.

Extra Innings' 12,000-square-foot baseball enclave sharpens batting and pitching skills with a lineup of seven multi-use training tunnels, plus baseball and softball lessons taught by current and former pros. Rent a batting tunnel for one hour ($35) and swing at an unlimited number of pitches flung by the ball-launching machines, which can be adjusted to spew out blazing fastballs for the pros or gentle, encouraging lobs that help to train new players. One tunnel boasts an Iron Mike pitching machine, which creates a realistic batting experience by winding up, releasing the ball, and simultaneously spitting out a cloud of partially masticated sunflower seeds. Good for a single player or an entire team, the batting tunnels are equipped with protective L-screens that allow teammates to sub in for Extra Innings' robotic all-stars and batters to face pitches lobbed by bona fide humans. To help hone hurling arms, pitching tunnels ($35/hour) let orb-slingers climb atop mounds and throw to a catcher, into a net, or to a live batter. Each of the spacious multi-use tunnels is 70 feet long, 20 feet high, and 15 feet wide, leaving plenty of room for wild pitches, fly balls, and improvement.

Extra Innings Miamisburg also leads one-on-one baseball and softball lessons taught by a staff of current and former professional ball players. The half-hour lessons ($35) are custom-tailored to each student's needs, using a step-by-step teaching approach to develop the skills needed to knock incoming pitches into the horizon, catch with the easy grace of a baseball-playing leopard, and throw curving pitches that whistle at the batter's least favorite pitch.