Rasmussen has 2 areas. Rasmussen West and The Lonely Boulder. Rasmussen West has more problems, most are short and some contrived. The Lonely Boulder is probably the biggest free standing boulder in the Mankato Area.
The problems are short but some are great. Enjoy.
Off 169 take the exit for Riverfront drive. Take Riverfront to the East until taking a right at the stoplight for Stoltzman road. Take Stoltzman for 1.3 miles, passing an obvious marsh, and then a right on an unmarked road that will lead you to Rasmussen Woods Nature Center. Park here.
For Rasmussen West, head to the South (left as you come in) and follow the trail around to the west. When arriving at the numerous forks in the trail, follow these directions: Left (straight), Right (straight), Left, Right. After taking these turns and dropping down into the marsh area, you will encounter the obvious cliff band.
For the Lonely boulder, head to the North (right as you come in) on an obvious trail. The boulder will be up and to the left after about 100 yards of hiking in (boulder is about 25 yards off the trail).
Mountain Project's determination of some of the classic, most popular, highest rated routes for Rasmussen Woods Boulders: