The Olympic Peninsula is really nice, but you might also want to drive east of the mountains, maybe go over Snoqualmie Pass, go down to Yakima through the Yakima River Canyon, then take White Pass back over to I-5, and north back to Seattle. I'd suggest either the North Cascades Highway, or Chinook Pass, but they are closed in winter and I don't believe either one has been reopened yet. I suppose another way to go would be over Snoqualmie Pass, and then north over Blewett Pass to Wenatchee. From Wenatchee go north to Chelan and if you have time all the way up to Winthrop. You should see lots of mule deer up that way, but no elk. Lots of elk down in the Yakima area, you could even stop by the elk feeding station at Oak Crek, on the way up to White Pass.