Monteith Park in Albany offers a lot; lawns, wooden docks, sandy/rocky beaches* and a wonderful jagged-rock* scene that's beautiful at sunset. There's a patch of woods and some paths and trails. The bridges between Downtown Albany and North Albany make a wonderful backdrop from the dock and beach areas. There is a public restroom in the park that's typically open year-around.
Monteith Park pairs well with Downtown Albany or the Albany Carousel if you're looking for a second location nearby.
*not accessible when water is high (typically November - May)