Tramvajová štola pod Špilberkem, Unfinished exploration adit in Brno, Czech Republic

Tramvajová štola pod Špilberkem is an unfinished geotechnical exploration adit in Brno, 510 metres long, driven through the Špilberk hill massif. Its lower portal was planned in the gap at the lower end of Pekařská Street, under Sladová Street, where the adit entrance lies. The intended tram tunnel would have curved right beneath the hill and emerged near today's Údolní, Marešovy and Joštovy streets, at about 650 metres.

In the late 1970s Brno's city leadership sought a fast tram link between Staré Brno and the centre, as the line along Pekařská Street lacked capacity. Survey work for the tunnel under Špilberk hill began in 1977, but the project was halted in 1979 for unclear reasons, possibly cost or unsuitable geology. The unfinished 510 m exploration adit was abandoned; the route remains reserved in Brno's territorial plan.

The tunnel represents an engineering attempt to modernize public transportation in Brno during the late 1970s through underground infrastructure development.

The tunnel entrance lies under Sladová Street at the lower end of Pekařská Street, where the planned lower portal was to stand. The 510 m adit is unfinished and not open to the public, so the entrance is the only part a visitor can reach. The route is still reserved in Brno's territorial plan for a future tram line.

Fissure springs run through the rock of the unfinished adit, and where surface water seeps through the cracks it becomes enriched with minerals. This produces sinter coatings, and stones encrusted with limestone gradually turn into "river pearls".