For generations, children have happily triggered their imaginations with die-cast train sets, wisely opting out of the fun-draining delays and baggage-handling mix-ups of toy airports. Create caravans of adolescent amusement with today's Groupon: for $30, you get $60 worth of electric toy trains and accessories from Lionel Electric Trains. After 110 years of packing Santa's physics-defying sack with child-delighting choo-choos, Lionel is offering direct access to its locomotive library by opening several temporary retail locations, including one at the Mall of America. Preschool conductors can practice plastic track transfers and chase off stowed-away snake-oil salesmen with the remote-controlled Little Lines train set ($59.99). Steam- and diesel-powered hobbyists can populate Lilliputian railways with a selection of meticulously detailed engines from every era, helicopter-holding flatbeds, working cranes, or turn-of-the-century passenger cabs filled exclusively with murder suspects. Outfit command hubs with the latest equipment in order to protect pets and miniature metropolises from malfunctioning iron horses.