The tunnels which carry Mill Run under downtown Meadville make for quite an adventure. The first tunnel begins near the hospital. The last tunnel (if you don't count the Route 19 bridge) terminates between Arch Street and the old City Hall building.
I traversed the tunnels as a volunteer on the French Creek Cleanup Day. The team that I was on was assigned to clean Mill Run between the hospital
and French Creek. Only one teammate and I walked the tunnels between
Park Ave and Arch St however, because the of the fast water that day. It
had rained during the night and was drizzling that day and Mill Run was
flowing brown and swiftly. We saw evidence that waters had touched or gotten
close to the ceiling of the tunnel in some places as recently as the last few years because there were small branches and other debris stuck to pipes
that went along the ceiling. This time it was only a couple feet deep
at most but there were also parts where the water was moving very
quickly over a smooth concrete floor and we had to keep crossing back
and forth to avoid deep eddies or raging torrents in certain places. I
would recommend a dry week as the optimal time for the tunnel walk.
The tunnels were interesting because in many places you could see the
bottoms of the buildings such as wood joists, water pipes, and
electrical wires. There is a house on the east side of Main Street
where the front porch sits above the creek. It is truly an underground tour of downtown Meadville.
Liberty Street to Park Ave:
The best place to start if you want to go downstream is on the south side of the Meadville Medical Center. There is a nice park that the hospital built with a pedestrian bridge, a brick pathway, and a nice grassy slope down to the creek. The creek goes through two large parallel metal tubes which take you under the hospital's maintenance building. Then you will be in a deep daylight section in the parking lot of the old Quick Fill station. There is a path that will allow you to get in or out here but it can be a little bit overgrown depending on the season. Continue down the tunnel under Liberty Street.
Once you go under Liberty Street, you will be beneath the Walgreens parking lot and then Walgreens itself. When you next emerge, you will be between Walgreens and a used appliance store on Garden Street. There is no access in or out here, just some sunlight. Continue down the tunnel under North Street.
Once you get under North Street, you will pass beneath some businesses and homes and you will be able to see the sky in some places. In particular, you will notice a high ceiling with some shafts of light visible just before you go under Main Street. This is the front porch of a house on the east side of Main Street. Next, go under Main Street in a new tunnel section which was constructed in 2010.
After passing under Main Street, you will go under the library garden and then out into daylight. There is easy access over some grass to W Steers Street. This is one of the longest daylight sections. After you pass under the intersection of Cottage and Walnut there is a narrow and rocky daylight section that goes between people's backyards. It can be overgrown with brush at times. Mickey's Fire House marks the end of this daylight section as the tunnels begin again.
Park Ave to Market Street:
Starting from Mickey's is where the tunnels really get exciting. This next tunnel runs all the way to Market Alley where there is a pedestrian bridge. Access in or out is difficult at Market Alley. Continuing down the tunnel it gets even better though. Here you can see some old sections of the tunnel and interesting parts of Meadville's past. There is a short waterfall which was very unnerving for me because the water was deep after it. I think I would have turned around except for the fact that my partner was trudging right along in front of me and we needed to stay together. Somewhere in this section is where the old French Creek Feeder Canal crossed Mill Run. When you come out, you will be in Mill Run Pocket Park behind Voodoo Brewery. You can get out of the creek here if you can find your way through the tall plants here.
Mulberry Street to Arch Street:
From Mill Run Pocket Park where we left off it is a quick jaunt under the parking structure to a shaft of daylight along the sidewalk of Water Street. Access in or out would be difficult here. One final tunnel will take you under Water Street, under the Big Lots parking lot, and then under Arch Street. When you emerge you will be right next to the old Meadville City Hall and adjacent to a monument to a native American (I forgot his name).
I hope that people can become more aware of these tunnels under Meadville because they adversely impact the water quality of Mill Run and subsequently French Creek. If people knew that Mill Run was right under Meadville and that the storm drains dump directly into it, maybe they would be more careful not to pollute it with chemicals and runoff from city streets.
Once you go under Liberty Street, you will be beneath the Walgreens parking lot and then Walgreens itself. When you next emerge, you will be between Walgreens and a used appliance store on Garden Street. There is no access in or out here, just some sunlight. Continue down the tunnel under North Street. 
Starting from Mickey's is where the tunnels really get exciting. This next tunnel runs all the way to Market Alley where there is a pedestrian bridge. Access in or out is difficult at Market Alley. Continuing down the tunnel it gets even better though. Here you can see some old sections of the tunnel and interesting parts of Meadville's past. There is a short waterfall which was very unnerving for me because the water was deep after it. I think I would have turned around except for the fact that my partner was trudging right along in front of me and we needed to stay together. Somewhere in this section is where the old French Creek Feeder Canal crossed Mill Run. When you come out, you will be in Mill Run Pocket Park behind Voodoo Brewery. You can get out of the creek here if you can find your way through the tall plants here. 
