Through the condo construction parking lot on the east side of the river at the dam. Go down the embankment and along the aqueduct, underneath the Dinosaur BBQ/old train station, and under the library. Look for the chain link fence on the right and the split in the fence where the red ladder is and climb down in.
Construction was being done on the area by the BBQ restaurant so I am not sure that it is safe or legal to go there. There was/is a gated/chained parking lot near the address off the main road that you could park at if it was open and walk down into the subway area. Haven't been there since I saw the construction which was 3-4 months ago.
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