The best and most obvious day trip from Llandudno is to Conwy, four miles to the east along the coast. Where Llandudno is Victorian and designed for pleasure, Conwy is medieval and designed for war: the UNESCO World Heritage castle built by Edward I in 1283–1289, the most complete set of medieval town walls in Britain, and the quayside harbour that has been the focus of the town's life for centuries. The contrast with Llandudno — two very different expressions of what a North Wales town can be — makes the combination of the two places particularly satisfying.
Conwy can be reached by car in ten minutes, by local bus, or by train (Conwy station is on the same line as Llandudno). The castle, managed by Cadw, is the centrepiece, but the town walls — which you can walk for much of their circuit — are equally impressive. The Smallest House in Britain on the quayside, Plas Mawr (the finest surviving Elizabethan town house in Wales), and Aberconwy House (medieval merchant's house, National Trust) add historical depth. A half day in Conwy is the minimum; a full day allows the walls, the castle and the quayside properly.
Bodnant Garden, about ten miles south of Llandudno in the Conwy Valley, is one of the finest gardens in Wales and among the best in Britain. Managed by the National Trust, the garden extends across 80 acres of hillside above the River Conwy, with formal terraces, wildflower meadows, a laburnum arch famous in May, and views across the valley to the Carneddau mountains. The journey from Llandudno to Bodnant via the Conwy Valley road is itself attractive, following the river through increasingly dramatic mountain scenery. The Bodnant Garden page covers the visit in more detail.
Betws-y-Coed is approximately 20 miles south of Llandudno, at the confluence of the Rivers Conwy and Llugwy at the edge of Snowdonia National Park. The village is the traditional gateway to the mountains and has the full complement of outdoor equipment shops, cafes, and visitor facilities that serve those heading further into the hills. The Swallow Falls waterfall, a short walk from the village, is one of the most visited natural sites in Wales. The Conwy Valley itself, between Llandudno and Betws-y-Coed, is worth driving slowly and stopping for the views.
The mountains of Snowdonia are visible from Llandudno on clear days, shaping the southern horizon beyond the Conwy estuary. Access to the heart of the national park from Llandudno takes 30 to 45 minutes by car, either through Betws-y-Coed and on to Capel Curig and Llanberis, or south through the Conwy Valley. The range of experiences within the park is extraordinary: from the summit of Snowdon (reachable by the Snowdon Mountain Railway from Llanberis, or on foot by several routes) to the lakeside walks of the Ogwen Valley, the slate quarries of Llanberis and the beaches of the Llyn Peninsula.
Snowdonia day trips from Llandudno work best with a car; public transport options exist but limit the flexibility to reach the more remote mountain destinations. A day in the mountains after a day by the sea, with the contrast of the Great Orme's accessible headland against the genuine high altitude of the Snowdonia peaks, is one of the pleasures of staying at Llandudno rather than further inland.
Colwyn Bay is approximately six miles east of Llandudno along the North Wales coast, a comfortable drive or bus journey. The town has its own Victorian promenade and pier (though the pier is in a different state from Llandudno's magnificently maintained example), beaches, and a town centre with its own independent shops and cafes. It is a day trip rather than a direct rival to Llandudno's attractions, but useful as a half-day addition to a longer visit.
Rhos-on-Sea, between Llandudno and Colwyn Bay, is a quieter residential seaside area with its own small harbour and boating lake. Deganwy, on the Conwy estuary directly opposite Conwy town, offers a peaceful waterside alternative with views across to the castle. Together, the immediate coastal strip east of Llandudno provides enough variety for a full week of day trips without going further than 15 miles.