These cost nothing and carry a full day each. Build around them and the paid tickets become optional extras instead of a budget drain.
Preseren Square and the Triple Bridge
FreeTipThe square is free and open at all hours, so see it twice: once at 8am when it is empty, and once after dark when the pink Franciscan church is floodlit. Plecnik widened a single stone bridge into three parallel spans in 1932, adding the two pedestrian side bridges to fan the crowds out toward the market, and standing on the outer arm gives you the shot with the church, the river and the castle in one frame.
TipThe walk up from the Old Town takes about 15 minutes on a steep wooded path and is free; the funicular from Krekov Square takes 60 seconds and costs a few euros, and a combined return plus attractions ticket is the better value if you want the viewing tower. Climb the tower rather than settling for the courtyard, because that is where you see the red roofs, the river bend and the Kamnik Alps on the horizon on a clear day. The grounds are open long hours, well past the ticketed exhibits, so sunset is free.
TipFour copper dragons have guarded this 1901 concrete bridge since it opened, and the dragon has been the city's symbol ever since, appearing on the coat of arms and on every souvenir in town. It is free and takes five minutes, so fold it into the walk between the Central Market and the station rather than making a trip of it; shoot from the riverbank below the bridge, not on it, because the traffic and the crowd on the deck ruin the angle.
National and University Library (NUK)
FreeTipPlecnik's 1941 masterpiece hides a dark stone staircase that climbs to a blaze of light at the reading-room door, a deliberate journey from ignorance to knowledge. The entrance hall and staircase are free to walk into during opening hours, but the great reading room itself is for cardholders and normally only opens to visitors in August, when the students are gone; guided tours run at other times, so ask at the desk rather than assuming you can wander in.
Cobblers' Bridge (Cevljarski most)
FreeTipPlecnik rebuilt this crossing in 1932 as a wide open platform ringed by columns, deliberately leaving it roofless so it works as a small square over the water rather than a route across it. It is free and permanently open, and it is the best spot in the city for a drink-in-hand pause between the two banks; the cobblers who gave it the name had their workshops on the medieval bridge here from the 13th century.
St Nicholas Cathedral
FreeTipEntry is free but the doors close over the middle of the day, roughly noon to 3pm, so time it for the morning or late afternoon. Look at the doors before you go in: the main bronze door was added for the Pope's 1996 visit and shows 1250 years of Slovenian Christianity in relief, while the side door carries the six bishops of Ljubljana, and both have been rubbed shiny where visitors touch them. Inside, the ceiling frescoes are the reason to look up.
TipThe city's big park starts a five-minute walk west of Preseren Square and runs straight up into the wooded Roznik hill, which is why Ljubljana keeps winning green-city awards. It is free and always open: walk Plecnik's broad Jakopic Promenade, where large-format photography is exhibited outdoors year-round, then keep climbing 20 minutes to the Roznik hilltop inn for a beer among locals walking their dogs.