There's no official entrance point to the Mljet National Park as such, and by the time you arrive in Polače or Pomena you're well already weinside it. However, you're expected to buy a ticket from one of the kiosks in Pomena,
Polace or just outside Govedari once you've settled in, and certainly before you start exploring. The kiosks also have park information and maps.
The park's main attractions are its two forest-shrouded "lakes" (actually inlets connected to the sea by narrow channels), Malo jezero ("Small and Veliko jezero ("Big Lake"), which together form a stretch of water some 4km long. Both are encircled by foot- and cycle paths, and the clear, blue-green waters are perfect for bathing. If you're staying in Polače, it's possible to walk over to the lakes by road or by well-signed forest path (via the 253-metre Montokuc hill) in about 45 minutes. From Pomena, Malo jezero is ten minutes' walk south, by way of a stone-paved footpath that heads over a wooded ridge just up from the port. Once you hit the shore of Malo jezero, it's another ten-minute walk to Mali most ("Little Bridge"), spanning the channel feeding into Veliko jezero, edged by magnificently soothing, tree-shaded pathways.
Mali most is the departure point for an hourly boat service (vouchers for the trip are included with the entrance ticket) down Veliko jezero to St Mary's Island (Otok svete Marije), where the Benedictines established a monastery in the twelfth century. Overlooked by a sturdy defensive tower, the monastery church features unusually chunky altarpieces carved from local stone and exuberantly coloured.The central dome is enclosed in a squat quadrangular tower, whose dog-tooth-patterned exterior can be admired from the neighbouring courtyard. There's a cafe-restaurant in the monastery grounds.
Bikes area handy way to get around the lakes: they can be rented from Mali most, the National Park kiosk in Polače, or in front of the Odisej hotel in Pomena. Kayaks can also be rented at Mali most.