Libreville's position on the coast and near several national parks makes it a good base for excursions, though some of these "day trips" are more honestly one- or two-night outings.
Pointe Denis is the easiest escape from the city. A 30-minute boat ride across the Gabon Estuary brings you to a sandy peninsula with quiet beaches and calm water. Pirogues and speedboats depart from the port area throughout the day. It is a popular weekend spot for Libreville residents, but during the week you may have the beach mostly to yourself.
Akanda National Park lies just north of Libreville and is accessible by boat from the city to the mouth of the Moka River. The park is mostly mangroves and tidal mudflats, and it is an important site for migratory birds. If you are a birder, this is an easy half-day trip. For others, the scenery is pleasant but not spectacular.
Pongara National Park sits on the southern shore of the Gabon Estuary, opposite Libreville. Between October and March, leatherback turtles nest along its beaches. The long Atlantic beach south of Pointe Denis is a quiet stretch of sand worth visiting even outside nesting season.
Lope National Park is reachable via the Trans-Gabon railway from Libreville, though the journey takes the better part of a day each way. A serious day trip it is not, but a two- or three-day visit is very doable. The park offers savanna and rainforest, large troops of mandrills, forest elephants, and gorillas. It is a UNESCO World Heritage Site and the most accessible of Gabon's major parks.
Ivindo National Park, further east along the railway, is home to thundering waterfalls and extraordinary wildlife clearings. Plan on at least two days. The train to Booue followed by a drive into the park is an adventure in itself.