During the bad times highways completely messed up Saint Paul. We're still recovering; only recently have we developed some north-south routes that safely cross rail and freeway.
Below are two examples that go between Macalester college and Como Park pavilion. It's about a 4.7 mile trip each way. From Como there are now quite good Grand Rounds trails west and east to Gateway (Stillwater).
These routes use some bike-pedestrian walkways over rail and freeway that are barely visible on Google maps and omitted from most paper maps.
UPDATE: The 2nd route, which is basically Griggs all the way, is excellent. Do that.
(Snelling may be impossible to cross, so consider going up to St Claire or down to Jefferson just before you reach Snelling)