This is Encil-Y-Mor, in Criccieth. It's a decent sized detached house, sleeps nine. Four bedrooms, two bathrooms, laid out over two floors. It's got a 4 Star rating, so it's comfortable and all the main things you'd need are included.
The house is in a quiet bit of a residential street, about five minutes' walk from the beach. The garden is lawned and not enclosed, so if you're bringing dogs you'll need to be mindful.
Now, the most important thing about this place is the stairs. They are steep, narrow, and have an open side. They're perfectly safe if you take care, but you need to know that upfront. It would be tricky for anyone unsteady on their feet.
The kitchen has a dishwasher and washing machine. Bedding and towels are included. Parking is right on site. The WiFi is fine. There's a TV and a shower over the bath.
The beach really is close. It's a good beach, proper sand and that castle view. There's a pub, a shop, and restaurants about half a mile up the road. Criccieth itself has the castle, a few good cafes, and proper fish and chips.
Porthmadog is a few miles away for a bigger supermarket, and that's where you can get the old Ffestiniog steam train up into the mountains. Portmeirion is nearby too, if you fancy a walk around there.
You're right on the edge of the Llyn Peninsula and Snowdonia is about a half hour drive for mountains and walks. There's a golf course locally.
You can bring up to three pets.
A few useful links for planning: Snowdonia National Park, Visit Wales North, and the National Trust page for Criccieth Castle.