The Třesín hill was first declared as a protected area in 1933 and was redeclared as a nature monument and national nature monument in 1993. The monument lies in the parishes of Mladeč and Bílá Lhota in the Olomoucký kraj – Olomouc Region. The national nature monument covers an area of 1ha and the Třesín Nature Monument covers 143 hectares.
The protected area consists of the predominantly forested Třesín hill (344.9 metres), which is built of karstified Devonian limestone with surface karst phenomena and cave systems. The Mladečské jeskyně Caves are a paleontological and archaeological proposed Site of Community Importance. The cave fauna includes several species of bat which hibernate here every year. The protected area also includes fragments of natural deciduous (beechwood) forest stands, and the locality represents the northern border of the range for several thermophilous herb species in Moravia.
The Třesín Threshold is built of strongly karstified Devonian Limestone, which is overlain by loess in places and by Quaternary gravels on the Morava river alluvial plain. The fault slopes fall into the fault-gap valley of the Morava river. Surface karst phenomena are found on limestone outcrops and these include dolines, limestone pavements and steep rocky cliffs above the valley plain. The extensive system of the Mladečské jeskyně was formed by the underground waters of the Hradečka and Rachava streams at three levels and has not yet been fully explored. Five karst springs (the Řimice Resurgences) emerge at the foot of Třesín hill on the north side. Rendzina and Fluvisol soil types cover the Třesín area.
A range of notable plant communities can be found on the Třesín Hill, including communities which are less common on the whole territory of the Litovelské Pomoraví PLA. These include oak-hornbeam forest with cow-wheat of the Melampyro nemorosi-Carpinetum association, oakwoods with wild service trees of the Sorbo torminalis-Quercetum association and calciphilous beechwoods of the Cephalanthero-Fagetum association. The flora at Třesín is characterised by the occurrence of calciphilous species, of which the rarest include the white helleborine (Cephalantheria damasonium) and narrow-leaved helleborine (Cephalantheria longifolia). A range of thermophilous species grow on the south-facing slopes. The Celtic rose (Rosa gallica), white stonecrop (Sedum album) and the blue-stem grass Bothriochloa ischaemum all have the northern border of their range in Moravia here at Třesín.
On the colder, northern slopes and shaded, rocky slopes we can find sub-montane species such as rattlesnake root (Prenanthes purpurea). Other interesting herbs which grow in the protected area include the western polypody (Polypodium interjectum), bastard balm (Melittis melissophyllum), self-heal or woundwort (Stachys recta), St. Bernard’s lily (Anthericum ramosum) and wood spurge (Tithymalus amygdaloides). The wild service tree (Sorbus torminalis) is a rarer tree species which grows in the protected area.
The fauna at Třesín has not been fully documented. A total of 33 species of terrestrial molluscs have been recorded here. Species which are bound to the limestone rocks include the rock snail Helicigona lapicida. The terrestrial gastropod Bythinella austriaca lives in the spring emergences. The caves provide a regular hibernating site for the greater mouse-eared bat (Myotis myotis), Daubenton’s bat (Myotis daubentonii), Geoffroy’s bat (Myotis emarginatus), barbastelle bat (Barbastella barbastellus), brown long-eared bat (Pleucotus auritis) and lesser horseshoe bat (Rhinolophus hipposideros).
Birds which are bound to the old deciduous forests on Třesín include the red-breasted flycatcher (Ficedula parva), stock dove (Columba oenas) and black woodpecker (Dryocopus martius). Both coloured forms of the red squirrel (Sciurus vulgaris) live here, as do the western hedgehog (Erinaceus europaeus), mole (Talpa europaea) and badger (Meles meles).
A marked tourist trail passes through the protected area and forms a 5.5km-long themed trail with information panels. The Mladečské jeskyně Caves with finds of Pleistocene fauna lie under the monument and are open to the public. This proposed archaeological Site of European Importance is best known for the discovery of the Mladeč man of the Aurignacien culture – the oldest known find of a modern humanoid in Europe.Similar discoveries are very rare in central and eastern Europe. The “Ve štole” Cave is used for speleotherapy.
Neoromantic structures from the middle of the 19th century such as the ruins of the “Rytířské síně – Chamber of the Knights”, “Čertův most – Devil’s Bridge” and the “Podkova – Horseshoe” cave or grotto can be visited on the forested limestone hill with fragments of natural forest stands.
The Třesín NNM is a part of the Litovelské Pomoraví proposed Site of Community Importance and SPA – Bird Area within the Natura 2000 network.