House Boat is a boat. A big, static one, on the creek in St Osyth. It's not a yacht, it's more like a floating cottage. You'll park at the boatyard and walk down the pontoon to get to it.
It sleeps two, in one bedroom. One bathroom. It's a 3 Star place, so it's clean and has what you need, but it's not fancy. It's on a pontoon, so you will feel it move a bit when the tide is high and it's windy. That's normal for a boat. It has a wood burner for the winter and the deck gets the sun in summer. You can bring one well-behaved dog.
The facilities are all there: TV, towels, parking. The electricity is included. There's no wifi, so you're properly switched off, which I think is the point.
You're right on the water. There's a footpath along the creek that goes out towards Point Clear. Across the creek is an aqua sports centre where you can hire kayaks or paddleboards, or try the inflatable water park.
St Osyth village is a walk away. It's got a shop, a couple of pubs for food, and a small harbour. The priory grounds and deer park are nice for a stroll. For a bigger beach, it's about three miles to Clacton or Walton. They have piers, amusements, that sort of thing.
Colchester is a twenty-minute drive. There's the castle museum, Castle Park with a boating lake, and all the usual shops. Colchester Zoo is about half an hour away.
For walks and planning, Essex Country Parks is useful, and Dedham Vale covers the Constable Country area just over the border in Suffolk.