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.
https://goo.gl/maps/yZimkd6AR2GacRdSA
and
https://goo.gl/maps/QZEa1atwCTiLwsXN7
(Snelling may be impossible to cross, so consider going up to St Claire or down to Jefferson just before you reach Snelling)
