A paleontological excursion could be organized in the Moscow Metro.
Fossils of inhabitants of ancient seas can be seen at the stations where the walls and columns are clad with limestone or marble. You wouldn't even need to use a magnifying glass to see them – their size varies from several centimeters to a half-meter.
Ammoniates, nautiluses, belemnites, sea lilies, sea urchins, brachiopods, gastropods, corals – all of them lived in seas millions of years ago, and now can be seen in the walls in the Moscow Metro.