What are your interests? City life, museums, nature, hiking, dinning, coffee, beer, wine, whiskey? Hard to recommend without more information.
Whale watching on Puget Sound Express out of Edmonds is usually a good bet to see some Orcas that time of year. The Minke’s, Gray’s and Humpbacks have mostly moved out of Puget Sound. If you like Espresso, get a Ristretto at Espresso Vivace and there are lots of other coffee options.
If you want to sample some Washington Wines, go to Woodinville where there are well over 100 tasting rooms and many more wineries. I’m sure there are a few breweries and distilleries in the area as well.
Seattle Center and Pike Place Market are a good bet for visitors as is a ride on a Ferry to one or more of many interesting destinations including the San Juan Islands.
Keep in mind Seattle is north of much of the US and days get shorter fast in October. Sunrise October 31st is 7:53 AM and Sunset is 5:52 PM. DST doesn’t end until November 3rd. Expect temperatures in the 50’s F, cloudy weather and periods of light rain. You might get lucky with good weather