Travelfree.info have found some cheap flights over at Ryanair and Wizzair web page to Porto (Portugal) flying from Riga just like this one departing on 14th January 2015 returning on 21st January 2015.
12:55 – 14:10 Riga – Dortmund (Wizzair)
22:50 – 22:40 Dortmund – Porto (Ryanair)
08:40 – 12:05 Porto – Brussels Charleroi (Ryanair)
17:05 – 20:30 Brussels Charleroi – Riga (Ryanair)
10kg 42x32x20cm x 1 units – free of charge. Backpack, bag or carrying case.
There are some great accommodation options listed on booking.com or if you are interested in booking apartment or room then visit airbnb.com (YOU WILL GET € 20 BONUS CREDIT FOR ACCOMMODATION after registration).
Have a look at Trip Advisor when planning your holiday to find out whats hot and whats not when it comes to all the local attractions.
To know more about Porto, you can visit and read more in Wikipedia here
To check more clear information about flights, check screenshots below: