Pwllheli is the traditional market-town of the beautiful Lleyn Peninsula (or in Welsh, Pen Llyn). The town is on the coast, with two sandybeaches(though the better beaches lie further down the lleyn, for example; Quarry a busy sandy beach, Hell's Mouth (Porth Neigwl in Welsh) a famous surfing beach and remote tranquil beaches like Porth Ysgo which has a 20' waterfall), a marina host to many Sailing regattas and as the market town has shops and cafés.
To find out more look at these sites:
http://www.llyn-wales.co.uk (on the whole of the lleyn)
http://www.penllyn.com (also on the Lleyn)
http://www.oriel.org.uk (The llanbedrog gallery website, this has a history of Pwllheli if you follow the "history link.")
http://www.britinfo.net/index_Pwllheli.htm (more commercial)
http://www.hafanpwllheli.co.uk (this is the mariner site, has useful tide times and weather.)
http://hen.gwynedd.gov.uk/adrannau/economaidd/busnesmarchnata/pwllheli/croeso/index.english.html (a biased account by Gwynedd council of Pwllheli and surrounding area)