Magical Mousehole is a delight but when at its busiest, the road down to this lovely fishing village can become a bottle-neck, and parking in the village is at a premium, as Mousehole existed centuries before the car.
The Harbour Authority has two car parks but parking is limited and roads to it are very narrow. North Quay Car Park is open all year and costs £5 a day. South Quay car park is not available in winter as it is used to store boats. In summer, it also costs £5 a day.
The Parade Car Park is slightly out of the centre (but not far to walk) costing just over £1 an hour. It has 80 spaces. Probably the best advice is to go early or later in the day before or after the crowds.
If the roads and car parks are full, you might be better off parking uphill at the village of Paul where you can normally park at the side of the road. It has a church and a pub, so is interesting in its own right, too. The walk down to Mousehole from there is lovely but the walk back up feels rather more taxing.