In adventures, after killing the boss, there would be a slim chance to be rewarded with an artefact. Explorers would have a slim chance to bring artefacts (not buffs). You could buy one for star coins. During holiday events (Christmas, Easter, Halloween, etc.) they could be bought for event items (pumpkins, eggs, presents) so everyone can have one. E.g. completing ten Christmas quests equals one artefact. Later, they could be acquired in other ways like logic puzzles, scavenger hunts, etc.

Two types of artefacts: one that can be traded and another that cannot be traded.

The non-tradeable artefacts are the ones that are unique for that artefact type. These have a stronger effect than the tradeable types. They could affect the whole island or all buildings or all buildings of the same type, each general or each geologist and their effect is constant. Every player can only have one of these - it's a matter of luck and effort. (Once in possession of the player, they cannot get it again, and the other artefacts' chances of being found would rise.) Not depending on the number of explorers sent out and the adventures played, only one could be found per week and per adventure.

Examples for artefact effects:
- woodcutters' production raised by 10%
- morale of the island raised by 5% (see this link: http://forum.thesettlersonline.com/t...-Morale-system)
- +5 building licences
- +5% accuracy to all military units.
- +1 hit points to all military units
- +n new settlers hourly
- +1 fish refill to all fish resource in every 10 minutes
etc.

Tradeable artefacts:
These are more localised, for example, they only affect one building (like an endless buff), one geologist/explorer/general. They only affect the building or specialist to which they are attached.
Examples:
- building's production time shortened by 20%
- general's all units attack in first strike (yes, this is a bit too strong, obviously it would not be an easy artefact to acquire)
- the explorer gets a donkey to transport its cargo and can bring back 50% more.

There can be many different bonuses, and not all of them need to be present in the game at the same time. A bit of variety never hurts.