Bac Lava: A cluster of little coves on the south side of Llanberis with walk-in entry (access these from the A4086).
The majestic lake railway passes by frequently on the far side of the shore, and what a site it is.
Viv Rickman: You can access Llyn Padarn easily from lots of different places. The Lagoons near Surflines are popular (free parking) and sheltered. They make for nice little journeys through the trees. If you plan to cross the lake it can get quite choppy in the middle on a windy day and you will certainly feel the temperature drop, it's pretty deep out there. End to end its roughly 3km if you fancy it... Very sociable lake with plenty of swimmers about in the triathlon season.
Be careful of the slate waste underfoot, it can slice bare feet quite badly!