Aquatic Park, operated by the City of Berkeley, provides a wide range of recreational opportunities, including bird-watching, boating, hiking, and the "Dream Land for Kids" play area, as well as a habitat for bird and aquatic life
Berkeley Aquatic Park would be my go-to choice! It's easy to access, there's a playground, and you can bike around the entire lagoon on a ped/bike path. You can add on trips over the highway to the Berkeley Marina or along the frontage road on the bay.
Aquatic park is just outside the area you mentioned. You can enter it near the 13/580 interchange: 2925 Bolivar Dr, Berkeley, CA 94710
It has a nice flat path that goes all the way around the mile-long lagoon, and at the north end it connects to the pedestrian/bike bridge that goes up over 80/580, which my 4-year old has been super excited about biking to the top of as an extra challenge.
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I had two birthday parties for my son at Aquatic Park in Berkeley. There is a picnic table directly next to the playground that is NOT reservable, but there are several picnic tables in the nearby field, a three-minute walk away, that ARE reservable, and this is what I did. It worked out well -- for some time, kids played together in the field, balls and frisbees and such, we had cake and lunch, etc. Then we moved to the wonderful playground. The only problem with this site is that it can be cool and windy. Nanu
Dreamland, the Robert Leathers playground at Aquatic Park in W Berkeley is a fabulous park which includes a toddler area. It is sandwiched between the train tracks & the water. Go west on Bancroft (a few blocks south of University Ave), past San Pablo, across the train tracks & turn right. It's about a block down, where the road ends in a parking area. mcherman
Go to Aquatic Park in Berkeley (near the freeway/water) for a great view of trains all afternoon long. We just went there for the first time with my partner's daughter who is nuts about trains and she loved it. It 's a fabulous playground and the tracks are only a short distance from the structures (it's a little loud when they go by..). She met her train quota for the month that one afternoon. Freyja
During his train phase, my son loved the playground at Aquatic park - I think it's called Dreamland. It's just west of the train tracks. The trains go by right behind the swings, and are visible from anywhere on the playground. To get there, take Bancroft 'til it ends and then go left until that street ends. Deborah
My son is also train obsessed. Two good spots are the great park along the estuary near University Avenue. Take 4th Street to Bancroft and go west, then turn left for about 1/8 of a mile. There is a wonderful new park with lots of great play structures. The train usually comes by 4 or 5 times while there. Kristi
Trainwatching is especially good at the kid's playground toward the south end of the Aquatic Park. From University Avenue, go south on 6th, then go west (towards the bay) on Bancroft. You'll cross the railroad tracks, and then after a block Bancroft ends at the Aquatic Park. Take a left on Bolivar and go a block or so to the end of it. You'll see a parking area and a big, new playground. It has both a toddler area and a bigger kids area. The train tracks run just to the east of it, separated from the play area by a fence. You can hear the trains coming, and then they go right by the playground -- very exciting Alysson