Ahhhh! Finally I know the answer to a WiD, but I don't get here first. :)

Anything fun on the other side of the walkway? I was poking around there a month ago on my lunch break but had to get back to work.

I've gone under 4th St - must have been after the flood, they were doing some kind of work on the culvert. Nice little area on the other side. I probably have a few snapshots somewhere. I didn't make it farther than that - the next culvert (presumably 3rd St) seemed pretty small - 3' square. Not hard to pass, but it didn't look like something to do on my lunch break. :)

Not sure if you'll make it all the way to the lake now - IIRC, there is some kind of gate on the lake side of the culvert that runs through I-35. There are also a few lights mounted that looked like signal lights of some sort. I figured they may have to do with releasing rain runoff into the stream and lake, but I don't know enough to really say.

@Nobody - Any other info about your trip would be appreciated - sounds fun!