Housed in a converted Thomas Telford-designed Parliamentary church on West Argyle Street, Ullapool Museum tells the story of the town and the surrounding northwest Highlands from pre-history to the present. The exhibits cover the geology of the ancient Torridonian sandstone landscape, the Norse settlers who named many of the local places, the fishing economy that has sustained Ullapool since the herring boom of the eighteenth century, and the Highland Clearances that emptied much of the interior.
The emigration section is particularly good. Ullapool was a major departure point for Highlanders forced off the land during the nineteenth century, and the museum holds records, photographs, and personal accounts of families who left for Canada, Australia, and New Zealand. It's a small museum but well curated and a good place to understand the landscape you're exploring.