If you are feeling the effects of too much Napa Valley wine, pack a picnic, your sturdiest shoes and a swimming costume, and head for Bothe-Napa Valley State Park. Striking out across the park’s grassy hillsides, studded by fir and pine trees and the easternmost groves of coastal redwoods, will soon clear the most hung-over head. Afterwards, relax by swimming a few lengths of the park’s public swimming-pool (open summer only).