Yes - the leaf formation indicates, it is the spiny bear's breech, Acanthus spinosus.

Interesting. It had very striking flowers and foliage. I have avoided planting any of these as I'd read they can be an aggressive spreader. Is that so? If it is, I may have to find a place where this can just do what it wants as I like it.

" I'd read they can be an aggressive spreader"

And I would say that the above photo is a pretty good indication of that, judging by the number of individual plants growing in that location!! The spread is via a creeping root system and any portion of root left behind when moving or attempting to remove these plants will rapidly result in a new plant. A difficult plant to be rid of if you decide you do not want.

Leaves are like those of Acanthus mollis (or a similar less divided species) and not like those of A. spinosus, which looks more like a thistle. The familiar A. mollis 'Latifolius' is a variant that is not representative of the typical species.

I'd take that with a grain of salt!! Acanthus mollis foliage is not nearly as highly divided as is the OP's photo and the lobes are not nearly as distinct.

Acanthus mollis:

garden web photos · More Info

Acanthus spinosus:

garden web photos · More Info

Your first photo is of A. mollis 'Latifolius' and not the typical A. mollis. And your second photo clearly shows what I was talking about, that the plant being asked about does not have the much divided, pointy looking (thistle-like) leaves of A. spinosus.

Your thinking here is apparently exactly what I assumed, that you think 'Latifolius' is the extent of A. mollis. And that you somehow cannot see that A. spinosus is much more divided etc. than the plant asked about.

From googling Acanthus mollis there do appear to be varieties with similar divided leaves, though when viewing my pic and spinosus side by side they are also very similar. An interesting side not to this is this planting is on the corner of NE 4th and 106th NE in Bellevue WA. It's a city planted roadside which are generally planted with annuals or perennials that will get removed and refreshed. I wonder if they know what they've put there and if they'll have trouble removing it.

Anyone try Acanthus "White Water"? So far it isn't doing much growing for me. Just put it in this Spring.

The leaves of Spiny Acanthus are more divided than those of the plant asked about. Regarding the 'Whitewater' it looks like there was a problem with the parental(?) variety lacking horsepower and this derivative(?) is supposed to be an improvement. But maybe that promise is not being borne out, and that is what you are seeing. Otherwise have you planted and observed other, green-leaved Acanthus in the same sizes at the same times of the year, so that you have a feeling for what is normal with these?

http://www.terranovanurseries.com/gardeners/acanthuswhitewater-p-239.html

Off-colored forms of acanthus - 'Hollard's Gold', Whitewater', Tasmanian Angel', etc. - seem to be not very robust and slow to establish and put on bulk. I have known a number of them to be planted in pretty much ideal acanthus conditions and the plants just dwindle away to nothing after a couple of seasons. Very shy to bloom as well.

Terra Nova claims 'Whitewater' is vigorous. See at above link.

Never planted a different acanthus in the PNW, but spent years trying to get every little piece of it out in So Cal. So I was surprised to see one just languish here. Back to the tried and true...