The Museo del Mare is housed in the halls of Palazzo Appiani, the former residence of the Lords of Piombino. Founded in 1985 at the initiative of the Commune and of the Piombino Institute of Biology and Marine Ecology within the context of a plan aimed at promoting tourism in the city, it proposes to study and monitor the marine environment of the Mediterranean. It is flanked by a Multipurpose Centre of Environmental Education, consisting of two sections, one dedicated to educational activities, the other to research. The Palazzo, equipped with sophisticated instrumentation for analysis and a system for filing and processing images, has recently acquired a system used to transmit images directly from the research laboratories to the projection rooms in real time. A specialised library and an aquarium consisting of 15 tanks connected to the sea through a pumping system are used to study the Mediterranean flora and fauna.

In the aquarium section is a small naturalist museum containing an interesting malacological collection, composed of Mediterranean shells, collected starting from 1980; among these, some are so tiny as to be visible only under a binocular microscope.