chef ownerfirst off, i would not choose " a really nice port" to reduce down you can achieve the same result with a middle of the road port and some... say honey , grape mollasses even some slow roasted grapes that you can cook down in the reduction.
but anyway what is done is done.
now you need to decide what direction you want to go with this reduction, sweet or savory.
go sweet and drizzle it over an italian prune plum gallette or fresh fig tart with some ice cream or try slow roasting some pears i mean slow let those sugars caramelize for a while; candy some nuts ( toasted first of course) hazelnuts or pinenuts you pick your favorite. then serve the port in dipping fashion along side this collection.
go savory and you have duck breast, pork tenderloin, lamb chicken if you prefer. use this reduction as a component in a gastrique with one of the afore mentioned fruits and knock the socks off your friends/family.
good luck good cooking good life