Wellnigh is an old fashioned word meaning almost. It's most often used in the phrase 'wellnigh impossible'.
It's wellnigh impossible to keep finding excuses to post pictures from my travels - but somehow I manage it!
Update - The concise Oxford dictionary gives this as one word, but other places list it as two, or even hyphenate it. All variants seem to have the same meaning. Nigh on its own means near.